[patch] Fix std::try_lock behaviour

[Jonathan Wakely]

On 22/09/14 15:54 +0100, Jonathan Wakely wrote:
>When I fixed std::try_lock a few years ago I misread the spec,
>exceptions should not be caught and turned into a return value.
>
>Tested x86_64-linux, committed to trunk.

... and also the 4.9 branch.

>    	* include/std/mutex (try_lock): Do not swallow exceptions.
>    	* testsuite/30_threads/try_lock/4.cc: Fix test.