7.x XML forms tests

This includes a suite of tests for XML Forms, including basic form management, association functionality, and some tests integrated with the Test Solution Pack.

One thing to note: the third commit down there slightly changes the way the Import Form form validates imported XML. This change was the best option to get the Import Form tests working, as SimpleTest's internal browser was uploading XML with an application/octet-stream mimetype.

This depends on the pull request at https://github.com/Islandora/islandora/pull/454