[v3] c++0x <thread>

[bkoz]

Yay. I am also pleased to see this functionality finally in after so
many months of discussion and work!!!! Great job Chris. Gcc-4.4 is in
a more coherent place now WRT the atomics and thread package.

I will re-generate the doxygen docs when I get back into town Saturday
night and put them up on gcc.gnu.org.

Paolo, I tested recent previous versions  of this on x86_64, seemed
good in both thread and --disable-thread configs. Wanted to test
darwin but having issues ATM. Thanks for putting this in!

At some point in the near future we have to figure out a way to
abstract out all the dg-options flags for enabling threads on each of
the supported targets. There's got to be a better way.

-benjamin