[Freeciv-Dev] (PR#7668) transporter types should be in the ruleset

["Jason Short" <jdorje@xxxxxxxxxxxxxxxxxxxxx>]

<URL: http://rt.freeciv.org/Ticket/Display.html?id=7668 >

Currently the transporter types are hard-coded.  There are three types 
of transporters:

   - Ground unit
   - Carrier (air unit + missile)
   - Missile (missile unit only)

which are specified for each unit in units.ruleset.  Of course the 
"missile" units have to be specified separately.

My idea (as described in PR#6174) is to generalize this to have 
arbitrary carrying types.  For instance units.ruleset could specify

   carry_types = "ground", "air", "missile"

and then for each unit the unit specifies

   cargo_type = "ground"

and for transporters the unit specifies

   transporter_types = "air", "missile"

This is not fully thought out, but I believe it will not only generalize 
the rulesets but will help to simplify the logic in some functions.

jason