rfc: give koji diff capabilities

[David Timms]

Probably thought of a million times, but was wondering whether it would 
be possible, and useful to give diff capabilities within the koji web 
interface.

eg: x86_64 build
...
Output  build.log  (tail)
         root.log (tail)
         state.log (tail)
could become:
Output  build.log  (tail)  (diff)
         root.log (tail)    (diff)
         state.log (tail)   (diff)

hovering over diff would cause a (json) load of options:
- diff -u with other arch:
   i686, ppc, ppc64
- diff -u with other version:
   list other builds in this release (eg devel): 4.3-1, 4.3-4,
- diff -u with other release:
   list other releases of same version that have been built: f12, f13

The diff could be generated to look like a viewvc side by side diff.
Bonus points if the diff ignores things like:
- tmp file names (/var/tmp/rpm-tmp.trZK8P)
- log address: 0x2b9c82662f90
- builder: x86-05.phx2.fedoraproject.org

Previously, I found the build logs rather boring; by saving each 
locally, then running meld on them, I immediately see what has changed 
between eg F12 and devel.

Any comments (other than 'show me the money/code') ?