Use escapejs on URL and captions for file attachments.

Most URLs are fine, but in the case where we're using authenticated URLs with
S3, we'll have &amp; in the URL where we wanted &.
Add support for Beanstalk as a hosting service.

This supports both Git and Subversion repositories on Beanstalk. It
makes use of the new base_commit_id support and hosting service
repository validation.

Unit tests were added for all the new functionality.