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.
#!/bin/sh
hg init
echo "nothing" > a
hg add a
hg commit -m ancestor -d "1000000 0"
echo "something" > a
hg commit -m branch1 -d "1000000 0"
hg co 0
echo "something else" > a
hg commit -m branch2 -d "1000000 0"
hg merge 1
hg id
cat a
hg status