Fixes, refactoring and new features

[fcrespel]

Hello,

Here are two small fixes for Ruby 1.8 and for the login button URL when Redmine is installed in a subdirectory (e.g. example.org/redmine)

[fcrespel]

While I was at it, I also implemented a few features I needed :

• Allow disabling CAS authentication globally.
• Allow replacing the default Redmine login page with CAS.
• On-the-fly user registration, with support for firstname/lastname/mail CAS attributes, self-registration form when attributes are missing, and association with an existing LDAP auth source in case you need to disable CAS later.

Feel free to pull/cherry-pick/rework this set of commits as you see fit :-)

[jbbarth]

Wow, that's a bunch of work, thanks! I'll try to test everything in the next 2 weeks and then merge it.

[jbbarth]

I cherry-picked 7 of the 8 first commits and pushed them to master.

I don't really understand a0a0bd2 : sure monkey patching is useful in Redmine plugins, but here OmniAuth accepts a proc for being dynamically configured, so I don't really see the point. Plus it changes the behaviour of the original code, which relies on Setting["host_name"] to avoid some reverse-proxy issues. Standard OmniAuth's full_host method has the usual problems in reverse-proxyfied environments IIRC.

The last 3 commits will be added soon but I want to add some tests for them, as the change is a bit more risky and needs to be maintained in future versions. I will post updates here.

Thanks again for all that work on the plugin!