[GameEngine] Commit all Kester's changes made to the gameengine to restore 2.25 like physics.

[SCons] Build with Solid as default when enabling the gameengine in the build process
[SCons] Build solid and qhull from the extern directory and link statically against them

That was about it.

There are a few things that needs double checking:

* Makefiles
* Projectfiles
* All the other systems than Linux and Windows on which the build (with scons) has been successfully tested.

source/gameengine/GameLogic/SCA_ISensor.cpp

@@ -156,6 +156,10 @@ PyMethodDef SCA_ISensor::Methods[] = {
 	 METH_VARARGS, GetUseNegPulseMode_doc},
 	{"setUseNegPulseMode", (PyCFunction) SCA_ISensor::sPySetUseNegPulseMode, 
 	 METH_VARARGS, SetUseNegPulseMode_doc},
+	{"getInvert", (PyCFunction) SCA_ISensor::sPyGetInvert, 
+	 METH_VARARGS, GetInvert_doc},
+	{"setInvert", (PyCFunction) SCA_ISensor::sPySetInvert, 
+	 METH_VARARGS, SetInvert_doc},
 	{NULL,NULL} //Sentinel
 };