First version of btInternalEdgeUtility to filter internal edge collisions.

See also http://code.google.com/p/bullet/issues/detail?id=27 for issue description and an example how to use this (a modified version of Bullet/Demos/ConcaveDemo)
This demo will be committed to Bullet/Demos/ConcaveDemo later.

src/BulletCollision/CollisionDispatch/btInternalEdgeUtility.h

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+
+#ifndef BT_INTERNAL_EDGE_UTILITY_H
+#define BT_INTERNAL_EDGE_UTILITY_H
+
+#include <LinearMath/btHashMap.h>
+#include "LinearMath/btVector3.h"
+
+///The btInternalEdgeUtility helps to avoid or reduce artifacts due to wrong collision normals caused by internal edges.
+///See also http://code.google.com/p/bullet/issues/detail?id=27
+
+class btBvhTriangleMeshShape;
+class btCollisionObject;
+class btManifoldPoint;
+class btIDebugDraw;
+
+///for btTriangleInfo m_flags
+#define TRI_INFO_V0V1_CONVEX 1
+#define TRI_INFO_V1V2_CONVEX 2
+#define TRI_INFO_V2V0_CONVEX 4
+
+#define TRI_INFO_V0V1_SWAP_NORMALB 8
+#define TRI_INFO_V1V2_SWAP_NORMALB 16
+#define TRI_INFO_V2V0_SWAP_NORMALB 32
+
+
+///The btTriangleInfo structure stores information to adjust collision normals to avoid collisions against internal edges
+///it can be generated using 
+struct	btTriangleInfo
+{
+	btTriangleInfo()
+	{
+		m_edgeV0V1Angle = SIMD_2_PI;
+		m_edgeV1V2Angle = SIMD_2_PI;
+		m_edgeV2V0Angle = SIMD_2_PI;
+		m_flags=0;
+	}
+
+	int			m_flags;
+
+	btScalar	m_edgeV0V1Angle;
+	btScalar	m_edgeV1V2Angle;
+	btScalar	m_edgeV2V0Angle;
+
+};
+
+typedef btHashMap<btHashInt,btTriangleInfo> btInternalTriangleInfoMap;
+
+
+///The btTriangleInfoMap stores edge angle information for some triangles. You can compute this information yourself or using btGenerateInternalEdgeInfo.
+struct	btTriangleInfoMap : public btInternalTriangleInfoMap
+{
+	btScalar	m_convexEpsilon;///used to determine if an edge or contact normal is convex, using the dot product
+	btScalar	m_planarEpsilon; ///used to determine if a triangle edge is planar with zero angle
+	btScalar	m_equalVertexThreshold; ///used to compute connectivity: if the distance between two vertices is smaller than m_equalVertexThreshold, they are considered to be 'shared'
+	btScalar	m_edgeDistanceThreshold; ///used to determine edge contacts: if the closest distance between a contact point and an edge is smaller than this distance threshold it is considered to "hit the edge"
+	
+	btTriangleInfoMap()
+	{
+		m_convexEpsilon = 0.00f;
+		m_planarEpsilon = 0.0001f;
+		m_equalVertexThreshold = btScalar(0.0001)*btScalar(0.0001);
+		m_edgeDistanceThreshold = btScalar(0.1);
+	}
+};
+
+
+
+///Call btGenerateInternalEdgeInfo to create triangle info, store in the shape 'userInfo'
+void	btGenerateInternalEdgeInfo (btBvhTriangleMeshShape*trimeshShape, btTriangleInfoMap* triangleInfoMap);
+
+
+///Call the btFixMeshNormal to adjust the collision normal, using the triangle info map (generated using btGenerateInternalEdgeInfo)
+///If this info map is missing, or the triangle is not store in this map, nothing will be done
+void	btAdjustInternalEdgeContacts(btManifoldPoint& cp, const btCollisionObject* trimeshColObj0,const btCollisionObject* otherColObj1, int partId0, int index0);
+
+///Enable the BT_INTERNAL_EDGE_DEBUG_DRAW define and call btSetDebugDrawer, to get visual info to see if the internal edge utility works properly.
+///If the utility doesn't work properly, you might have to adjust the threshold values in btTriangleInfoMap
+#define BT_INTERNAL_EDGE_DEBUG_DRAW
+
+#ifdef BT_INTERNAL_EDGE_DEBUG_DRAW
+void	btSetDebugDrawer(btIDebugDraw* debugDrawer);
+#endif //BT_INTERNAL_EDGE_DEBUG_DRAW
+
+
+#endif //BT_INTERNAL_EDGE_UTILITY_H