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.
adding a
adding b
adding c
% should succeed
200 Script output follows
/al/
/b/
/c/
200 Script output follows
a
200 Script output follows
b
200 Script output follows
c
% should fail
404 Not Found
error: repository circle not found
404 Not Found
error: repository circle not found
404 Not Found
error: repository circle not found
% collections errors