Log Message:
update to 2.2.12,
fix MASTER_SITES
changes:
* gtkmm 2.2.10 had an incorrect configure-time test, that mistakenly
  disabled some template code for gcc, used to convert from
    intermediate C++ containers to STL containers. For instance, this
      broke the gnome-vfsmm build.
* TreeView::get_path_at_pos(): Correct memory management. ("David").
* ConstructParams::ConstructParams(): improvement. (Daniel Elstner).
* TreePath::append(): Maybe fixed compilation for gcc 3.4. (Daniel Elstner)