fix in btParallelConstraintSolver to support double precision

fixes in SAT/polyhedral contact clipping, avoid adding GJK contacts (the contact margin causes different contact depths)
add polyhedral convex shape in InternalEdgeDemo as example of the new SAT/polyhedral contact clipping (added reference to Manual/what's new)
avoid glueing objecs with contacts that are positive (no gaps)

src/LinearMath/btPoolAllocator.h

@@ -62,6 +62,11 @@ public:
 		return m_maxElements - m_freeCount;
 	}
 
+	int getMaxCount() const
+	{
+		return m_maxElements;
+	}
+
 	void*	allocate(int size)
 	{
 		// release mode fix