rhg: Accept different "invalid ignore pattern" error message formatting
At the moment rhg compiles all patterns into a single big regular expression,
so it’s not practical to find out which file the invalid bit of syntax
came from.
Differential Revision: https://phab.mercurial-scm.org/D11942
#
# Avoid interference from actual test env:
unset HGTEST_JOBS
unset HGTEST_TIMEOUT
unset HGTEST_PORT
unset HGTEST_SHELL