- make the bool in logformat an enum: "doesn't care about logging begin",
   "should log begin if it hasn't been logged yet", and "should assert
   that the begin was already logged"
 - make logging client code not try to log commits, prepares, or aborts
   for read-only txns
 - added test, fixed another test


git-svn-id: file:///svn/toku/tokudb@44651 c7de825b-a66e-492c-adef-691d508d4ae1