swift234

[ClangImporter] Don't put method redeclarations in a member list.

Previously we'd try to put the same method into the list of members multiple
times--once for each redeclaration in the @interface. This led to an
assertion failure.

Checking the canonical decl isn't super cheap, but the ObjCMethodDecl
redeclaration infrastructure seems to be fairly broken. We can revisit this
later.

There's also a test for what happens when categories get involved. I'm not
convinced this is correct behavior, either, and will file an additional bug
to look into that at some point.

rdar://problem/19039485

Swift SVN r24129