Merge pull request #240 from erwincoumans/master

allow to compile using gcc-4.x on Mac OSX
AMD 14.50Alpha5 driver fixes the issue with MPR kernel, re-enable testFileFracture.bullet
call 'updateCamera' in GpuDemos.
Add serialization support for btGeneric6DofSpring2Constraint
Attempt to re-order serialization data so it can be serialized in-memory (for deep copy)