swift234

[Protocol conformance] Select the most specialized witness for a requirement.

Previously, we would consider (say) a generic witness and a
non-generic witness to have equal weight when selecting a witness,
then fail with an ambiguity. Instead, use the same
"more-specialized-than" logic used by overloading to select the most
specialized witness. Fixes <rdar://problem/14650915>.


Swift SVN r6960