type_traits: Implement is_function.

2004-12-16  Paolo Carlini  <pcarlini@suse.de>

	* include/tr1/type_traits: Implement is_function.
	(struct __sfinae_types, struct __is_function_helper): New.
	* testsuite/tr1/4_metaprogramming/composite_type_traits/
	is_object/is_object.cc: New.
	* testsuite/tr1/4_metaprogramming/composite_type_traits/
	is_object/typedefs.cc: Likewise.
	* testsuite/tr1/4_metaprogramming/primary_type_categories/
	is_function/is_function.cc: Likewise.
	* testsuite/tr1/4_metaprogramming/primary_type_categories/
	is_function/typedefs.cc: Likewise.

From-SVN: r92258