Added a possibility to build appGpu2dDemo with CUDA solver.

It is disabled by default, see Demos/Gpu2dDemo/btGpuDemoDynamicsWorld.h for instructions how to enable it

Cleaned up Extras/CUDA folder and libbulletcuda project

Extras/CUDA/btGpuDemo2dCudaFunc.cu

@@ -0,0 +1,46 @@
+/*
+Impulse based Rigid body simulation using CUDA
+Copyright (c) 2007 Takahiro Harada  http://www.iii.u-tokyo.ac.jp/~takahiroharada/projects/impulseCUDA.html
+
+This software is provided 'as-is', without any express or implied warranty.
+In no event will the authors be held liable for any damages arising from the use of this software.
+Permission is granted to anyone to use this software for any purpose, 
+including commercial applications, and to alter it and redistribute it freely, 
+subject to the following restrictions:
+
+1. The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgment in the product documentation would be appreciated but is not required.
+2. Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
+3. This notice may not be removed or altered from any source distribution.
+*/
+
+#include <cstdlib>
+#include <cstdio>
+#include <string.h>
+
+#include "cutil_math.h"
+#include "math_constants.h"
+
+#include <vector_types.h>
+
+//----------------------------------------------------------------------------------------
+
+#include "btCudaDefines.h"
+
+//----------------------------------------------------------------------------------------
+
+#include "../../src/BulletMultiThreaded/btGpuUtilsSharedDefs.h"
+#include "../../Demos/Gpu2dDemo/btGpuDemo2dSharedTypes.h"
+#include "../../Demos/Gpu2dDemo/btGpuDemo2dSharedDefs.h"
+
+//----------------------------------------------------------------------------------------
+
+texture<float4, 1, cudaReadModeElementType> posTex;
+
+//----------------------------------------------------------------------------------------
+
+#include "../../Demos/Gpu2dDemo/btGpuDemo2dSharedCode.h"
+
+//----------------------------------------------------------------------------------------
+//----------------------------------------------------------------------------------------
+//----------------------------------------------------------------------------------------
+