Create test_log6a_abort.c.   Returns {{{ENOMEM}}} from {{{r = toku_lt_acquire_write_lock(db->i->lt, toku_txn_ancestor(txn...)...)}}} in ydb.c:2126.  Addresss #536.  Maybe also Addresses #501. (?).

git-svn-id: file:///svn/tokudb@2932 c7de825b-a66e-492c-adef-691d508d4ae1