How to update a tileset from 3.0 to 3.1

To update a tileset from 3.0 to 3.1 you must add some new graphics and update the file format strings.
==The .tilespec file==
* Set format of .tilespec file to options = "+Freeciv-3.1-tilespec"
* There's a new layer InfraWork that you need to add to your layer_order
* Add stack_size_offset_x and stack_size_offset_y for offsets of the unit stack size sprites (automatically generated sprites)
==The .spec files==
* Set format of all .spec files to options = "+Freeciv-3.1-spec"
* Rename unit.irrigate as 'unit.cultivate, or have them both as aliases for the same sprite if you still want to support rulesets that have not done their part of the rename.