contrib.texi (Contributors): Add Paolo Carlini and Janis Johnson.

	* doc/contrib.texi (Contributors): Add Paolo Carlini and
	Janis Johnson.
	Update Richard Henderson, Jakub Jelinek, and Mark Mitchell.
	Refer to Objective-C instead of ObjC, SPARC instead of sparc,
	and CPU instead of cpu.

From-SVN: r52893