tests/helper-runtests.sh

rust-status: check for '.hg' regardless of file type (issue6300)

'.hg' would show up in `hg status` if were a symlink.

Differential Revision: https://phab.mercurial-scm.org/D8461

#
# Avoid interference from actual test env:

unset HGTEST_JOBS
unset HGTEST_TIMEOUT
unset HGTEST_PORT
unset HGTEST_SHELL