c++: name-lookup refactoring

c++: name-lookup refactoring

Here are some refactorings to the name-lookup machinery.  Primarily
breakout out worker functions that the modules patch will also use.
Fixing a couple of comments on the way.

	gcc/cp/
	* name-lookup.c (pop_local_binding): Check for IDENTIFIER_ANON_P.
	(update_binding): Level may be null, don't add namespaces to
	level.
	(newbinding_bookkeeping): New, broken out of ...
	(do_pushdecl): ... here, call it.  Don't push anonymous decls.
	(pushdecl, add_using_namespace): Correct comments.
	(do_push_nested_namespace): Remove assert.
	(make_namespace, make_namespace_finish): New, broken out of ...
	(push_namespace): ... here.  Call them.  Add namespace to level
	here.