mod_assignment has been replaced with a stub that only exists to support restoring and
auto upgrading to mod_assign. If you require mod_assignment for some old plugin, then
overwrite with the 2.6 version manually.
Solution is as follows:
* Allow unsupported subplugins to convert from Moodle1 to Moodle2
* On Moodle2 restore hide unsupported subplugins
* Graceful error message in assignment of unsupported subplugins
Sam Hemelryk