next: also use stack shortcut in output when possible
This mirror what `hg evolve` is doing since cc3a0b13ae57.
# utility to setup pythonpath to point into the tested repositoryexportSRCDIR=`dirname$TESTDIR`if[-n"$PYTHONPATH"];thenexportHGTEST_ORIG_PYTHONPATH=$PYTHONPATHexportPYTHONPATH=$SRCDIR:$PYTHONPATHelseexportPYTHONPATH=$SRCDIRfi