Update rubygems source
Fix mocha setup
Remove rdoc tasks, I can't be bothered
Replace class_inheritable* with class_attribute

None of these are mutable structures, so straight replacement should be fine
Force Rails 3.1 for testing

We will migrate to globalize3 before we go to Rails 3.2, so we
don't need to fix anything for that.
Trivial test fixes

Wow Rails 3.1 reveals a lot of assert statements that were supposed
to be assert_equal statements.