rewind: update the working copy if it gets obsoleted
If the working copy parent is rewinded, follow the rewind.
# utility to setup pythonpath to point into the tested repositoryexportSRCDIR=`dirname$TESTDIR`if[-n"$PYTHONPATH"];thenexportHGTEST_ORIG_PYTHONPATH=$PYTHONPATHexportPYTHONPATH=$SRCDIR:$PYTHONPATHelseexportPYTHONPATH=$SRCDIRfi