trac integration -- cross link trac changesets with buildbot

[zooko]

(From the #trac channel on IRC.)

<zooko> You know what would be really cool?  If when looking at a changeset, 
        like this -- http://allmydata.org/trac/tahoe/changeset/2513 -- I could 
        click a link and go to the automated builds of that changeset, like 
        this -- 
        http://allmydata.org/buildbot/waterfall?show_events=false&first_time=1209061000&last_time=1209063500

<zooko> And vice versa -- when looking at the buildbot (the second URL), it 
        would be great to have a link to the changeset on trac (the first URL). 

[marcusl]

A hook for the latter would be nice. Just a way to replace the changes-page generation with a function of my own, taking some suitable parameters, would suffice. (This could either generate HTML or just send a redirect to a trac-url). Then users could configure their buildmasters according to their VCS and Trac/Redmine?/whatnot software.

The first might be trickier, as we might not know when a changeset was pushed (for CVCS it's the same time as commit, for DVCS not so), unless we had a mapping of changes<->builds somewhere, enabling .../waterfall?revision=xxxxxxxxxx URLs.

(Sprintwise, I vote for the first.)