* doc/xml/manual/status_cxx2017.xml: Document P0156R2 status.
	* doc/html/*: Regenerate.
	* include/std/mutex (scoped_lock): Implement new C++17 template.
	* testsuite/30_threads/scoped_lock/cons/1.cc: New test.
	* testsuite/30_threads/scoped_lock/requirements/
	explicit_instantiation.cc: New test.
	* testsuite/30_threads/scoped_lock/requirements/typedefs.cc: New test.

From-SVN: r245903