Crash bug when "mesh" applied twice fixed

Constraints reworked - all of them could now work with one or two bodies

Modification of constraint frames and initial positions of rigid bodies
now allowed at start frame only

Plugin version is set to 2.76

src/BulletDynamics/ConstraintSolver/btGeneric6DofConstraint.cpp

@@ -53,6 +53,19 @@ m_useSolveConstraintObsolete(D6_USE_OBSOLETE_METHOD)
 }
 
 
+static btRigidBody s_fixed(0, 0, 0);
+btGeneric6DofConstraint::btGeneric6DofConstraint(btRigidBody& rbB, const btTransform& frameInB, bool useLinearReferenceFrameB)
+        : btTypedConstraint(D6_CONSTRAINT_TYPE, s_fixed, rbB),
+		m_useSolveConstraintObsolete(false),
+		m_frameInB(frameInB),
+		m_useLinearReferenceFrameA(useLinearReferenceFrameB)
+{
+	///not providing rigidbody A means implicitly using worldspace for body A
+	m_frameInA = rbB.getCenterOfMassTransform() * m_frameInB;
+}
+
+
+
 
 #define GENERIC_D6_DISABLE_WARMSTARTING 1