swift234

Enforce semantic requirements for protocols and @mutating.

- @mutating is not allowed in classbound protocols (already implemented, new testcase though).
- @mutating protocol methods can be implemented by class methods (which aren't allowed to be @mutating).
- @mutating protocol methods can be implemented by struct methods that are @mutating or not.
- @mutating struct methods do not conform to non-@mutating requirements.

I think this covers everything.



Swift SVN r11787