swift234

fix <rdar://problem/20167543> "for var x = ..." not parsed as a foreach loop

This was because the ambiguity between c-style and foreach loops wasn't being
properly handled.  Use the canParsePattern() logic to handle this in full 
generality.

Since that logic was unused, dust it off and clean it up a bit.  Similarly,
remove some old vestigates of default argument parsing in tuples and 
old-syntax array handling.



Swift SVN r26164