topic: make revsets like 'foo#stack[0]' work
'stack' relation subscript function is another way to refer to s0, s1, etc. But
instead of aborting in many cases it will simply return an empty set.
# utility to setup pythonpath to point into the tested repository
export SRCDIR=`dirname $TESTDIR`
if [ -n "$PYTHONPATH" ]; then
export HGTEST_ORIG_PYTHONPATH=$PYTHONPATH
export PYTHONPATH=$SRCDIR:$PYTHONPATH
else
export PYTHONPATH=$SRCDIR
fi