tests: make test-extension.t's baduisetup.py test fail even if bdiff exists
A mercurial.bdiff module has existed at some point and when I have
built at an old version, some .pyc file or something seems to stick
around and test-extension.t fails. Let's remove the reference to bdiff
and simplify the test.
Differential Revision: https://phab.mercurial-scm.org/D1162
Issue351: mq: qrefresh can create extra revlog entry
$ echo "[extensions]" >> $HGRCPATH
$ echo "mq=" >> $HGRCPATH
$ hg init
$ hg qinit
$ echo b > b
$ hg ci -A -m foo
adding b
$ echo cc > b
$ hg qnew -f foo.diff
$ echo b > b
$ hg qrefresh
$ hg debugindex b
rev offset length ..... linkrev nodeid p1 p2 (re)
0 0 3 ..... 0 1e88685f5dde 000000000000 000000000000 (re)