[v3] c++0x <mutex> and <condition_variable>

[Paolo Carlini]

Chris Fairles wrote:
> Perhaps for now we shouldn't define _GTHREADS_CXX0X in gthr-posix.h
> unless _POSIX_TIMERS > 0 ? (attached patch plus changelog).
>   
Nope. We should just not rely *in the library* on anything requiring 
pthread_mutex_timedlock if the macros is not defined > 0. Or, in case 
it's defined as == 0 we should check at run time. But the gthr-posih.h 
is ok as is.

For now, for darwin, I'm going to add _POSIX_TIMERS > 0 in the macros 
protecting the headers, but we need something more fine grained, around 
specific functions in the implementation requiring pthread_mutex_timedlock.

Paolo.