Fix static media URLs when running the devel server with a SITE_ROOT.

The way that static media URLs ('/static/' and '/media/') were mapped when a
SITE_ROOT was defined was problematic, in that it was appending the SITE_ROOT
twice in the urlspec. The problem is that all the URLs were created with the
root prepended, but the way that settings.py defined the urls didn't have the
right distinctions between the names of the directories and the URL paths.

Testing done:
Tested that loading the dashboard included all static media with a SITE_ROOT of
both '/' and '/example/'.
Merge branch 'release-1.7.x'
Expand review when jumping to comment from issue table.

When clicking on an issue in the issue table, we bring the user to the
associated comment. This wasn't working if the comment was part of a review
that had been collapsed. Now we expand the appropriate review before sending
the user to the comment.

Fixes issue #3770.
Assert that a comment is passed to CommentDialogView.

At some point before committing my CommentDialogView change, logic
leading to an assertion moved, which we needed to ensure that there was
some comment passed to CommentDialogView. The assertion is now added to
CommentDialogView.create, which first references the comment.
Models for Depends On feature have been added to reviews/models.py

Specifically, the ManyToMany relationships between Draft ->
(Draft/Published) and Published -> (Draft/Published) have been
mapped.

The Depends On project is now at a stage where the visual front end
is prepped, and the database modelling has been initially completed.
Merge branch 'master' of git://github.com/reviewboard/reviewboard into depends