tests/helper-runtests.sh

revset: add test for resolution of infix/suffix ambiguity of x^:y

This is the test for 805651777188, and I'm going to fix the failure of
'x^A' where 'revsetalias.A=:y'.

#
# Avoid interference from actual test env:

unset HGTEST_JOBS
unset HGTEST_TIMEOUT
unset HGTEST_PORT
unset HGTEST_SHELL