Fix a subtle buffer overflow in the membuffer cache when the data buffer size is not a multiple of 16 bytes (ITEM_ALIGNMENT).  Because we will move the insertion pointer always in multiples of ITEM_ALIGMENT, it could then be moved to a position behind the buffer where capacity - position < 0.
Fix a subtle buffer overflow in the membuffer cache when the data buffer
size is not a multiple of 16 bytes (ITEM_ALIGNMENT).  Because we will
move the insertion pointer always in multiples of ITEM_ALIGMENT, it could
then be moved to a position behind the buffer where capacity - position < 0.

Also, fix two small style and spelling issues.

* subversion/libsvn_subr/cache-membuffer.c
  (insert_entry, move_entry): add assertions to debug overflows in future
  (ensure_data_insertable): make condition immune to overflows
  (svn_cache__membuffer_cache_create): actual fix
  (drop_entry): minor formatting fix
  (membuffer_cache_set_internal): fix typo

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion