revsetlang: perform quoting using ui.escapestr instead of repr()
This changes one of the doctest results, but I'm pretty sure on
inspection that it's an equivalent result.
#require test-repo
$ . "$TESTDIR/helpers-testrepo.sh"
$ cd "$TESTDIR"/..
New errors are not allowed. Warnings are strongly discouraged.
$ hg files "set:(**.py or **.txt) - tests/**" | sed 's|\\|/|g' |
> python contrib/check-config.py