compat: conditionally access config item
Version 4.2 and below do not have config items support. So the extensions helper
do not register anything.
# utility to setup pythonpath to point into the tested repositoryexportSRCDIR=`dirname$TESTDIR`if[-n"$PYTHONPATH"];thenexportHGTEST_ORIG_PYTHONPATH=$PYTHONPATHexportPYTHONPATH=$SRCDIR:$PYTHONPATHelseexportPYTHONPATH=$SRCDIRfi