gcc atomic word

[Valient Gough]

I didn't see a link for archives of this list, so I don't know if this 
has been discussed.

I have uploaded a patch to commoncpp2-1.3.1 which adds support for gcc's 
_Atomic_word counter (in bits/atomicity.h).
Changes:

- m4/ost_pthread.m4 is modified to check for support
- configure.ac is modified to specify C++ as the language to use for 
tests (I don't know why it wasn't already, since this is a C++ library)
- include/cc++/thread.h and src/mutex.cpp are modified with the 
implementation.

I've only verified that it correctly detects support for my compiler and 
builds, nothing more.

regards,
Valient