versioncontrol 5.x-1.0-rc3

Fix a few issues (including some rather severe ones) that I discovered while starting the Subversion backend:

• Postgres support should be working now.
• Make sure that the versioncontrol_delete_{repository,branch,tag,commit}() functions work from [vcs_backend]_uninstall().
• Make sure that disabled backends never cause *more* results to be retrieved by the query functions. Do not use more than one backend without upgrading to this release, as it might delete your version control related data on uninstalling a backend.
• Make sure that the FakeVCS backend never handles form value extraction hooks if it hasn't altered the form beforehand.
• Fix a typo in the FakeVCS backend.
• Polish for the repository edit form: require a repository name, and remove a duplicate form element description.