Sort out two -Wdeprecated-copy warnings

- SMaterial copy constructor is removed entirely
  (same change in upstream trunk r6362)
- CMatrix4 gets an explicit, but default copy constructor readded

include/matrix4.h

@@ -102,6 +102,9 @@ namespace core
 			//! Simple operator for linearly accessing every element of the matrix.
 			const T& operator[](u32 index) const { return M[index]; }
 
+			//! Sets this matrix equal to the other matrix.
+			CMatrix4<T>& operator=(const CMatrix4<T> &other) = default;
+
 			//! Sets all elements of this matrix to the value.
 			inline CMatrix4<T>& operator=(const T& scalar);