3578: Use something besides alert modal dialogs for error messages when publishing review requests

What version are you running?

2.1 alpha 0 (dev)

What's the URL of the page containing the problem?

Any review request page.

What steps will reproduce the problem?
1. With the patch from https://reviews.reviewboard.org/r/6322/ applied, create a review request and publish it.
2. Alter the review request by editing the description, adding a character, pressing OK. The green publish bar should be shown.
3. Alter the review request again to remove the character you added - the review request should be the same as it was after you first published it, but the publish bar should still be around.
4. Publish the review request.

What is the expected output? What do you see instead?

An error dialog is shown in an alert dialog. That's what issue 3452 was supposed to fix, and it does it fine - but I think we should use something other than an alert dialog for these errors.

What operating system are you using? What browser?

OS X 10.8, Firefox Nightly (35.0a1)

Please provide any additional information below.