Added a gCompoundChildShapePairCallback to filter (enable/disable) child shape collisions for a btCompoundShape.

Thanks to Rich McDaniel for the patch.
See MyCompoundChildShapeCallback in Demos/ConvexDecompositionDemo/ConvexDecompositionDemo.cpp for usage.

src/BulletCollision/CollisionDispatch/btCompoundCollisionAlgorithm.cpp

@@ -11,6 +11,9 @@ 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.
+
+VERSION alterations
+2013-Mar-21: Rich McDaniel - Added callback function to eliminate collisions based on shape testing
 */
 
 #include "BulletCollision/CollisionDispatch/btCompoundCollisionAlgorithm.h"
@@ -22,6 +25,8 @@ subject to the following restrictions:
 #include "btManifoldResult.h"
 #include "BulletCollision/CollisionDispatch/btCollisionObjectWrapper.h"
 
+btShapePairCallback gCompoundChildShapePairCallback = 0;
+
 btCompoundCollisionAlgorithm::btCompoundCollisionAlgorithm( const btCollisionAlgorithmConstructionInfo& ci,const btCollisionObjectWrapper* body0Wrap,const btCollisionObjectWrapper* body1Wrap,bool isSwapped)
 :btActivatingCollisionAlgorithm(ci,body0Wrap,body1Wrap),
 m_isSwapped(isSwapped),
@@ -129,6 +134,12 @@ public:
 		childShape->getAabb(newChildWorldTrans,aabbMin0,aabbMax0);
 		m_otherObjWrap->getCollisionShape()->getAabb(m_otherObjWrap->getWorldTransform(),aabbMin1,aabbMax1);
 
+		if (gCompoundChildShapePairCallback)
+		{
+			if (!gCompoundChildShapePairCallback(m_otherObjWrap->getCollisionShape(), childShape))
+				return;
+		}
+
 		if (TestAabbAgainstAabb2(aabbMin0,aabbMax0,aabbMin1,aabbMax1))
 		{