Refs #1531.    The fix is don't compile {{{test_txn_abort6}}} under BDB, rather than hacking around with the #ifdefs inside the code.  I noticed this because the main line wouldn't compile tonight.

git-svn-id: file:///svn/toku/tokudb@10513 c7de825b-a66e-492c-adef-691d508d4ae1