tests: allow more detailed error message from re.compile
test-grep.t now passes on Python 3.
Differential Revision: https://phab.mercurial-scm.org/D4240
%include map-cmdline.default
[templates]
changeset = '{cset}{branches}{bookmarks}{tags}{lphase}{parents}{luser}{ldate}{summary}\n'
changeset_verbose = '{cset}{branches}{bookmarks}{tags}{lphase}{parents}{luser}{ldate}{lfiles}{lfile_copies_switch}{description}\n'