graphlog: split the actual DAG grapher out into a separate method
This allows extensions like pbranch to use asciigraph() to graph dependencies
for patch branches, but could be used for basically any DAG.
echo % setting up repo
hg init test
cd test
echo a > a
hg ci -Ama
hg rm a
hg ci -mdel
echo % set up hgweb
hg serve -n test -p $HGPORT -d --pid-file=hg.pid -A access.log -E errors.log
cat hg.pid >> $DAEMON_PIDS
echo % revision
"$TESTDIR/get-with-headers.py" localhost:$HGPORT '/rev/tip'
echo % diff removed file
"$TESTDIR/get-with-headers.py" localhost:$HGPORT '/diff/tip/a'