SCONS: Darwin build flag changed
SCONS: Darwin build flag changed

Removed c++11 from the build flags.  There was a reason this was added in earlier osx versions to allow it to build, but thats not the case now and the reasons are lost to time.

Safe to remove following testing with unit tests, pub / sub, capturereplay / mamalistenc testing (QPID 0.11)

dpauls/OpenMAMA,fquinner/OpenMAMA,philippreston/OpenMAMA,fquinner/OpenMAMA,dpauls/OpenMAMA,fquinner/OpenMAMA,dpauls/OpenMAMA,fquinner/OpenMAMA,dpauls/OpenMAMA,fquinner/OpenMAMA,dpauls/OpenMAMA,philippreston/OpenMAMA,philippreston/OpenMAMA,philippreston/OpenMAMA,dpauls/OpenMAMA,philippreston/OpenMAMA,philippreston/OpenMAMA,fquinner/OpenMAMA,fquinner/OpenMAMA,philippreston/OpenMAMA,dpauls/OpenMAMA