Tileset tags for cultivate/plant actions
Attached patch does not touch Mine/Plant case. Instead Irrigate/Cultivate case is made equivalent to it; Cultivate uses "unit.cultivate" and Irrigate has that as a fall back. It's assumed that most of the time Irrigate/Mine have extra specific sprites available.
In other words this patch renames "unit.irrigate" as "unit.cultivate". Supplied tilesets are set up to still provide "unit.irrigate" as an alias of "unit.cultivate", to support rulesets that are using "unit.irrigate" as alt tag for extra building activity sprite.
Cultivate and Plant actions currently share their tileset tag names with Irrigate/Mine default graphics. This means that tag for Cultivate is "unit.irrigate", and one for Mine is "unit.plant". Sort that out.