utils/large_bitset: Fix buffer overflow in load()/save()
utils/large_bitset: Fix buffer overflow in load()/save()

Also fixes https://github.com/cloudius-systems/seastar/issues/54

==5658==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x6250006b7848 at pc 0x1413e02 bp 0x7fff7cd7f1e0 sp 0x7fff7cd7f1d8
WRITE of size 8 at 0x6250006b7848 thread T0
    #0 0x1413e01 in unsigned long* std::__copy_move<false, false, std::random_access_iterator_tag>::__copy_m<std::_Deque_iterator<unsigned long, unsigned long&, unsigned long*>, unsigned long*>(std::_Deque_iterator<unsigned long, unsigned long&, unsigned long*>, std::_Deque_iterator<unsigned long, unsigned long&, unsigned long*>, unsigned long*) /usr/include/c++/4.9/bits/stl_algobase.h:336
    #1 0x1413c59 in unsigned long* std::__copy_move_a<false, std::_Deque_iterator<unsigned long, unsigned long&, unsigned long*>, unsigned long*>(std::_Deque_iterator<unsigned long, unsigned long&, unsigned long*>, std::_Deque_iterator<unsigned long, unsigned long&, unsigned long*>, unsigned long*) /usr/include/c++/4.9/bits/stl_algobase.h:396
    #2 0x1413aea in unsigned long* std::__copy_move_a2<false, std::_Deque_iterator<unsigned long, unsigned long&, unsigned long*>, unsigned long*>(std::_Deque_iterator<unsigned long, unsigned long&, unsigned long*>, std::_Deque_iterator<unsigned long, unsigned long&, unsigned long*>, unsigned long*) /usr/include/c++/4.9/bits/stl_algobase.h:434
    #3 0x14138df in unsigned long* std::copy<std::_Deque_iterator<unsigned long, unsigned long&, unsigned long*>, unsigned long*>(std::_Deque_iterator<unsigned long, unsigned long&, unsigned long*>, std::_Deque_iterator<unsigned long, unsigned long&, unsigned long*>, unsigned long*) /usr/include/c++/4.9/bits/stl_algobase.h:466
    #4 0x1413545 in unsigned long* std::__copy_n<std::_Deque_iterator<unsigned long, unsigned long&, unsigned long*>, unsigned long, unsigned long*>(std::_Deque_iterator<unsigned long, unsigned long&, unsigned long*>, unsigned long, unsigned long*, std::random_access_iterator_tag) /usr/include/c++/4.9/bits/stl_algo.h:779
    #5 0x1412d44 in unsigned long* std::copy_n<std::_Deque_iterator<unsigned long, unsigned long&, unsigned long*>, unsigned long, unsigned long*>(std::_Deque_iterator<unsigned long, unsigned long&, unsigned long*>, unsigned long, unsigned long*) /usr/include/c++/4.9/bits/stl_algo.h:804
    #6 0x14112b3 in unsigned long large_bitset::load<std::_Deque_iterator<unsigned long, unsigned long&, unsigned long*> >(std::_Deque_iterator<unsigned long, unsigned long&, unsigned long*>, std::_Deque_iterator<unsigned long, unsigned long&, unsigned long*>, unsigned long) utils/large_bitset.hh:81
    #7 0x13fcfc9 in _ZZZN8sstables7sstable11read_filterEvENKUlRT_E_clINS_6filterEEEDaS2_ENKUlvE_clEv (/home/tgrabiec/src/urchin/build/debug/scylla+0x13fcfc9)
    #8 0x1400a50 in apply /home/tgrabiec/src/urchin/seastar/core/apply.hh:34
    #9 0x1400afb in apply<sstables::sstable::read_filter()::<lambda(auto:25&)> [with auto:25 = sstables::filter]::<lambda()> > /home/tgrabiec/src/urchin/seastar/core/apply.hh:42
    #10 0x1400bb2 in apply<sstables::sstable::read_filter()::<lambda(auto:25&)> [with auto:25 = sstables::filter]::<lambda()> > /home/tgrabiec/src/urchin/seastar/core/future.hh:1062
    #11 0x140f1b7 in _ZZN6futureIIEE4thenIZZN8sstables7sstable11read_filterEvENKUlRT_E_clINS2_6filterEEEDaS5_EUlvE_S0_EET0_OT_ENUlOS4_E_clI12future_stateIIEEEEDaSC_ (/home/tgrabiec/src/urchin/build/debug/scylla+0x140f1b7)
    #12 0x140f350 in run /home/tgrabiec/src/urchin/seastar/core/future.hh:359
    #13 0x426e2c in reactor::run_tasks(circular_buffer<std::unique_ptr<task, std::default_delete<task> >, std::allocator<std::unique_ptr<task, std::default_delete<task> > > >&, unsigned long) core/reactor.cc:1093
    #14 0x429cb1 in reactor::run() core/reactor.cc:1190
    #15 0x72bc69 in app_template::run_deprecated(int, char**, std::function<void ()>&&) core/app-template.cc:122
    #16 0xa119bc in main /home/tgrabiec/src/urchin/main.cc:279
    #17 0x7ffc1b6beec4 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21ec4)
    #18 0x412558 (/home/tgrabiec/src/urchin/build/debug/scylla+0x412558)

0x6250006b7848 is located 0 bytes to the right of 8008-byte region [0x6250006b5900,0x6250006b7848)
allocated by thread T0 here:
    #0 0x7ffc1cf6c7df in __interceptor_malloc (/usr/lib/x86_64-linux-gnu/libasan.so.1+0x547df)
    #1 0x7ffc204eef17 in operator new(unsigned long) (/usr/lib/x86_64-linux-gnu/libstdc++.so.6+0x8df17)
    #2 0xfa5d4f in large_bitset::large_bitset(unsigned long) utils/large_bitset.cc:15
    #3 0x13fcec6 in _ZZZN8sstables7sstable11read_filterEvENKUlRT_E_clINS_6filterEEEDaS2_ENKUlvE_clEv (/home/tgrabiec/src/urchin/build/debug/scylla+0x13fcec6)
    #4 0x1400a50 in apply /home/tgrabiec/src/urchin/seastar/core/apply.hh:34
    #5 0x1400afb in apply<sstables::sstable::read_filter()::<lambda(auto:25&)> [with auto:25 = sstables::filter]::<lambda()> > /home/tgrabiec/src/urchin/seastar/core/apply.hh:42
    #6 0x1400bb2 in apply<sstables::sstable::read_filter()::<lambda(auto:25&)> [with auto:25 = sstables::filter]::<lambda()> > /home/tgrabiec/src/urchin/seastar/core/future.hh:1062
    #7 0x140f1b7 in _ZZN6futureIIEE4thenIZZN8sstables7sstable11read_filterEvENKUlRT_E_clINS2_6filterEEEDaS5_EUlvE_S0_EET0_OT_ENUlOS4_E_clI12future_stateIIEEEEDaSC_ (/home/tgrabiec/src/urchin/build/debug/scylla+0x140f1b7)
    #8 0x140f350 in run /home/tgrabiec/src/urchin/seastar/core/future.hh:359
    #9 0x426e2c in reactor::run_tasks(circular_buffer<std::unique_ptr<task, std::default_delete<task> >, std::allocator<std::unique_ptr<task, std::default_delete<task> > > >&, unsigned long) core/reactor.cc:1093
    #10 0x429cb1 in reactor::run() core/reactor.cc:1190
    #11 0x72bc69 in app_template::run_deprecated(int, char**, std::function<void ()>&&) core/app-template.cc:122
    #12 0xa119bc in main /home/tgrabiec/src/urchin/main.cc:279
    #13 0x7ffc1b6beec4 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21ec4)

SUMMARY: AddressSanitizer: heap-buffer-overflow /usr/include/c++/4.9/bits/stl_algobase.h:336 unsigned long* std::__copy_move<false, false, std::random_access_iterator_tag>::__copy_m<std::_Deque_iterator<unsigned long, unsigned long&, unsigned long*>, unsigned long*>(std::_Deque_iterator<unsigned long, unsigned long&, unsigned long*>, std::_Deque_iterator<unsigned long, unsigned long&, unsigned long*>, unsigned long*)
Shadow bytes around the buggy address:
  0x0c4a800ceeb0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c4a800ceec0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c4a800ceed0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c4a800ceee0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c4a800ceef0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x0c4a800cef00: 00 00 00 00 00 00 00 00 00[fa]fa fa fa fa fa fa
  0x0c4a800cef10: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c4a800cef20: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c4a800cef30: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c4a800cef40: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c4a800cef50: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07
  Heap left redzone:       fa
  Heap right redzone:      fb
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack partial redzone:   f4
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Contiguous container OOB:fc
  ASan internal:           fe
==5658==ABORTING

capturePointer/scylla,senseb/scylla,scylladb/scylla,bowlofstew/scylla,respu/scylla,respu/scylla,rentongzhang/scylla,shaunstanislaus/scylla,kjniemi/scylla,aruanruan/scylla,kangkot/scylla,senseb/scylla,gwicke/scylla,raphaelsc/scylla,rluta/scylla,dwdm/scylla,tempbottle/scylla,kangkot/scylla,capturePointer/scylla,avikivity/scylla,eklitzke/scylla,acbellini/scylla,bowlofstew/scylla,dwdm/scylla,wildinto/scylla,stamhe/scylla,gwicke/scylla,raphaelsc/scylla,scylladb/scylla,dwdm/scylla,justintung/scylla,bowlofstew/scylla,linearregression/scylla,senseb/scylla,rluta/scylla,acbellini/scylla,aruanruan/scylla,duarten/scylla,guiquanz/scylla,victorbriz/scylla,stamhe/scylla,scylladb/scylla,duarten/scylla,duarten/scylla,kangkot/scylla,glommer/scylla,shaunstanislaus/scylla,phonkee/scylla,kjniemi/scylla,kjniemi/scylla,gwicke/scylla,raphaelsc/scylla,aruanruan/scylla,justintung/scylla,phonkee/scylla,avikivity/scylla,phonkee/scylla,avikivity/scylla,victorbriz/scylla,asias/scylla,linearregression/scylla,acbellini/scylla,shaunstanislaus/scylla,guiquanz/scylla,scylladb/scylla,capturePointer/scylla,rluta/scylla,asias/scylla,glommer/scylla,rentongzhang/scylla,victorbriz/scylla,asias/scylla,eklitzke/scylla,eklitzke/scylla,stamhe/scylla,rentongzhang/scylla,linearregression/scylla,wildinto/scylla,justintung/scylla,tempbottle/scylla,guiquanz/scylla,respu/scylla,glommer/scylla,tempbottle/scylla,wildinto/scylla