There are unfortunately times when upgrading Review Board is not as simple as running "svn up." We've so far been unhelpful with this. Now that we're going to require some changes for the media locations and users aren't necessarily going to see the message on the listserv, I felt we should have a nice way of communicating to the user.

This change introduces the ability to add checks on startup. These may include schema changes in the future, but right now they check if the media setup is what we expect. If not, an error page is displayed with helpful information. Once the user fixes the problem and restarts Review Board, the normal URLs will be activated.

This can also be useful for first-time users who currently have very little aid.

Tried this change with a branch using the old media setup and saw that it told me how to fix the problem instead of taking me to any URLs.

Tried it on a branch with the new media setup and Review Board operated as normal.