refactor: extract obs fate algorithm from _getobsoletereason Refactor _getobsoletereason to extract the obs fate computation into a separate function, it will be used later and put it in obshistory as it will be needed in other files. Rename _getobsoletereason to _getobsoletefateandsuccessors.

# 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