Backport the cheaper Preserve/Release on channels.
Updated package "platform" to version 1.0.13.  Separated the
identifiers "macosx*-i386-x86_64" and "macosx-universal" as
incompatible with each other.

Plus addition of a cast in tclIO.c to match types in a comparison
which otherwise bugs a Windows debug build (warnings are errors).
merge-mark
Updated package "platform" to version 1.0.13.  Separated the
identifiers "macosx*-i386-x86_64" and "macosx-universal" as
incompatible with each other.
Addition of a cast in tclWinFile.c to match types in a comparison, and
fix of a TRACE string literal in tclExecute.c with a bogus escape. Both
would otherwise bug a Windows debug build (where warnings are errors).
Another Preserve/Release on channels is needed during IO finalization.
Another Preserve/Release on channels is needed during IO finalization.
merge trunk