Add support for displaying list of changesets and ranges of changesets in TracRevisionLog by extending the TracLinks `log:` syntax.
Now, in addition to a single range `[12:23]` which was already supported, one can list multiple ranges like `[12:34,45:50]` (or equivalently `[12-34,45-50]`). Single changeset numbers can also be listed instead of ranges, e.g. `[1,2,3-6,10,11]`.
