These failures are mostly because of enabling the commented out
transaction code - the roundup testsuite doesn't expect to have to call
save_index() to commit changes, but that is required when transactions
are used.  I've no idea how this is intended to work, so I just disabled
transactions again for now, and updated the comments instead.

There was however a mistake in the docid attribute change I made.  I've
attached an updated patch which makes roundup trunk r4483 pass with both
Xapian 1.0.12 and 1.2.2.