Fix python2.3 incompatibility introduced by
a2b13cac0922.
run-tests.py: Make tests run with python2.3 if HGTEST_* is set.
optparse of python2.3 does not transform default values to the specified
type so e.g. "HGTEST_JOBS=4" (introduced in
07c3cd695b48) causes tests
to abort, because options.jobs is set to '4' instead of the number 4.