console: support for multiple codebases.

Changes / Effects:

1) Only the changes in a build is used to compare with the changeset revision.
The revision id from got_revision is not used.

2) If there are multiple builds with the matching changeset the first one
found is used. So if a slave is lost the build is marked as exception. Then
when the build is restarted that will be used instead.

3) Fixed it from loading all builds when multiple codebases is used.
console: check codebase is in build before checking revisions
console: hide box if codebase of change is not in builder.
Merge branch 'console-multi-codebase' of git://github.com/thedylman/buildbot
add relnotes