mathtils, convenience attributes added 'row' and 'col', this makes the row/col swap a lot easier to deal with, since

now you can still use column access

previously...
  mat[2] = 1, 2, 3

needed to be converted into...
  mat[0][2] = 1
  mat[1][2] = 2
  mat[2][2] = 3

but with column access you can do...
  mat.col[2] = 1, 2, 3


Having 'row' attribute is a bit redundant since direct indexing on a matrix uses row but included for completeness.

source/blender/python/mathutils/mathutils_Matrix.h

@@ -35,6 +35,7 @@
 #define MATHUTILS_MATRIX_H
 
 extern PyTypeObject matrix_Type;
+extern PyTypeObject matrix_access_Type;
 #define MatrixObject_Check(_v) PyObject_TypeCheck((_v), &matrix_Type)
 #define MATRIX_MAX_DIM 4