Implement diagnostic stream operator for ParsedAttr.

As a part of attempting to clean up the way attributes are 
printed, this patch adds an operator << to the diagnostics/
partialdiagnostics so that ParsedAttr can be sent directly.

This patch also rewrites a large amount* of the times when
ParsedAttr was printed using its IdentifierInfo object instead
of being printed itself.  
*"a large amount" == "All I could find".

llvm-svn: 339344