fixes in Jam msvcgen -> use SSE instead of SSE2 to stay compatible with older AMD Athlon XP processors, updated build files, minor compile fixes for GPU experimental code

Demos/Box2dDemo/Jamfile

@@ -0,0 +1,3 @@
+SubDir TOP Demos Box2dDemo ;
+
+BulletDemo Box2dDemo : [ Wildcard *.h *.cpp  ] ;