[Freeciv-Dev] RFC: tech lease treaty

["Per I. Mathisen" <per@xxxxxxxxxxx>]

This patch implements a new treaty similar to shared vision. It allows
sharing technology in a way that I've chosen to call "lease technology".

Basically, someone you lease your technology to can build any units,
wonders and city improvements that you can build, but your enemies cannot
steal those techs from that player. That player can research leased
technologies at half research cost.

This opens up a host of interesting multiplayer options. (For example it
removes the annoyance of opening up the diplomacy dialog every other turn
to give your warfaring allies your latest, greatest technologies.)

Since that player must know what techs you have before a tech lease treaty
becomes useful, he/she must have an embassy before such a treaty can be
made to him/her.

This patch implements the necessary diplomacy dialog changes for gtk1
client only.

Two questions that need to be answered:
 - I have not implemented a "withdraw lease" button anywhere, so for now,
once made, a lease agreement cannot be broken. This is because I felt the
player dialog was too crowded already, so I didn't know where to put it.
 - A part of the concept of "lease" is that the leasing out party gets
something in return. The most natural thing would be gold. However, when
and how this should be deducted from the leasing party I don't know.
Perhaps an extra 1 gold upkeep each turn from each city producing
something that requires a leased tech that goes to the leasing out party?

Comments wanted.

  - Per

lease1.diff
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