[PATCH 0 of 1 RFC] hgweb: graphing files using revsets

[timeless]

I think i have revsets graphing files.

Some people think i should try to use the revsets functions directly instead of building a string.
I tried to do that and got stuck trying to figure out how to call revset.sort().

This stuff is really far afield from the work I need to do, so as I already spent a night looking
into it, I'm punting. If someone wants to use revset.*(), they can probably convert this code
faster than I wrote it or tried to port it.