chrono (duration): Use explicitly defaulted ctor, cctor, dtor and assignment.

chrono (duration): Use explicitly defaulted ctor, cctor, dtor and assignment.

2008-07-31  Chris Fairles <chris.fairles@gmail.com>

        * include/std/chrono (duration): Use explicitly defaulted ctor, cctor,
	 dtor and assignment. Add diagnostics as per 20.8.3 paragraphs 2, 3
	 and 4 in WD. Other minor tweaks.
        * testsuite/20_util/duration/cons/1_neg.cc: Adjust line numbers.
	* testsuite/20_util/duration/requirements/typedefs_neg1.cc: New.
	* testsuite/20_util/duration/requirements/typedefs_neg2.cc: Likewise.
	* testsuite/20_util/duration/requirements/typedefs_neg3.cc: Likewise.

From-SVN: r138434