In most cases this means adding @public to things that get serialized;
in a few cases it means using a modern public stdlib API instead of
a legacy thing I was trying to keep @internal.
Swift SVN r19350
This includes proper rules for function overloads (i.e. shadowing by type)
and allowing type lookup to find a type even if it has the same name as
a non-type.
lookupVisibleDecls does not use this behavior yet.
Swift SVN r7016
