Most tests were using %swift or similar substitutions, which did not
include the target triple and SDK. The driver was defaulting to the
host OS. Thus, we could not run the tests when the standard library was
not built for OS X.
Swift SVN r24504
These types are often useless and confusing to users who expect to be able to use Sequence or Generator as types in their own right like in C# or Java. While we're here, relax the rules for self-conformance to admit methods returning 'Self'. Covariant return types should not actually prevent a protocol type from conforming to itself, and the stdlib makes particular use of protocols with 'init' requirements which implicitly return Self.
Swift SVN r18989
