type_traits: Implement is_convertible.

type_traits: Implement is_convertible.

2005-02-23  Paolo Carlini  <pcarlini@suse.de>

	* include/tr1/type_traits: Implement is_convertible.
	* testsuite/tr1/4_metaprogramming/relationships_between_types/
	is_convertible/is_convertible.cc: New.
	* testsuite/tr1/4_metaprogramming/relationships_between_types/
	is_convertible/typedefs.cc: Likewise.
	* testsuite/testsuite_tr1.h: Add class DerivedType.

	* include/tr1/type_traits (is_function): Don't mistake references
	to function types for function types.
	* testsuite/tr1/4_metaprogramming/primary_type_categories/
	is_function/is_function.cc: Add testcase.

From-SVN: r95458