tests/helper-runtests.sh

tests: run many tests in $TESTTMP/repo instead of $TESTTMP

This is useful so we can store other files in $TESTTMP
(in particular tests that use docket files (nodemap, dirstate-v2) keep
file uids in $TESTTMP/UID)

#
# Avoid interference from actual test env:

unset HGTEST_JOBS
unset HGTEST_TIMEOUT
unset HGTEST_PORT
unset HGTEST_SHELL