I would leave the transaction issue for now then - roundup will work
just as well with the second patch applied as it does currently, but
with the added bonus of working with Xapian 1.2.x, which beats breaking it.

It's quite possible whoever wrote this code thought they wanted to use
transactions, but found they weren't implemented at the time, and left
that commented out code there despite it not being needed at all.

The comments about why the transaction code isn't used are at least more
correct now, should anyone want to investigate in the future.