Fix for memory corruption and segfaults.
Fix for memory corruption and segfaults.

See convention #3 at http://code.google.com/p/leveldb/source/browse/include/leveldb/c.h
The *errptr must be NULL, but previously that was not always so, because Haskell alloca, while allocates memory, does not zero-fill it.

kernelim/leveldb-haskell,agrafix/rocksdb-haskell,kernelim/leveldb-haskell,kernelim/leveldb-haskell,kernelim/leveldb-haskell