r340: Fix http://bugs.mysql.com/bug.php?id=18283 in ha_innodb.cc and
http://bugs.mysql.com/bug.php?id=18238 in InnoDB

r339: Remove disk space leak on update of BLOB columns (Bug #18252).

btr_cur_pessimistic_update(): Invoke rec_get_offsets() after
rec_set_field_extern_bits().

btr_store_big_rec_extern_fields(): Note that offsets will no longer be
valid after calling this function.

r338: Fix bug 18238 : check in pessimistic insert and update if the buffer
pool is exhausted by locks