pthread_mutex_t initializer idiom

[Benjamin Kosnik]

I'm still trying to unify some of the atomics and concurrency code, and
remove duplicates.

I see this idiom a lot:

	  __gthread_mutex_t temp = __GTHREAD_MUTEX_INIT;
	  _M_mutex = temp;

Can somebody explain to me why we are doing this instead of:

_M_mutex = __GTHREAD_MUTEX_INIT;

?

Is this something to do with the gthread abstraction layer and POD mutexes?

-benjamin