Add migrate control to Auth.wiki()

The Auth.wiki() function does not allow for control of the migration
settings, always defaulting to migrate=True. In some instances the
developer may want to not force migration. This change adds the
ability to set the migrate option. Fake_migrate was not added but
can be if desired.
Merge pull request #72 from grutz/auth_wiki_migrates

Add migrate control to Auth.wiki()