Code review comment for lp:~asc/fluidity/extrudeup

The extrude branch has been updated.

- Added back in the removed preprocessing step
- Ensured the align_with_geoid option works when the domain is spread over multiple partitions
- Added more accurate control over the position of the horizontal layers
- Removed some debugging ewrites

This is now complete, except for a description in the manual.
I'll send out an update of developments to everyone.