Bug#340407: freeciv-server: Auto Settlers should not move on unsave terrain.

[Jacob Nevins]

Control: retitle -1 Auto Settlers should not move on unsafe terrain.

Roman Bertle wrote (Nov 2005, 2.0.7-1):
> if the "Auto Settler" command is given to a settler, worker or
> engineers, the unit moves also on unsave terrain such as glacier, and is
> in high risk to be lost.

The notion of unsafe terrain on which units randomly die was removed
upstream in 2007 (2.2.0, git 63e024da5c), so this is now moot.

Karl Goetz wrote (Feb 2010, 2.1.10):
> Subject: they also move other places
> like next to enemy units, for nations you are at war with.

A brief history of autosettlers' response to threats:

A very long time ago, there was a rather hacky notion of keeping out of
the way of enemy units, that reportedly didn't work very well and was
removed entirely in 2.1.0 (git 69d8d63253, RT PR#12977; "v.2 of the
patch. Autosettlers now fear no evil.")

After that, they learned not to wander into unfriendly territory
(borders) in 2.2.0 (git d0516f2a77, gna bug #14614).

They learned not to pick dangerous worksites and to stop working in the
face of immediate threat in 2.4.0 (git 9186857c3d, gna patch #3384),
using a rather simple and imperfect threat model (notably, only taking
land units into account).

This was made a little more sophisticated in 2.5.0 (git cdb73ed11a,
gna patch #3854), notably taking sea units into account.

They have not learned to avoid danger en route to a worksite (was gna
patch #3383), or consider threats based on attacker movement rate rather
than fixed distance etc (was gna bug #20587, gna patch #3383).

Still, I think there has been sufficient progress since this ticket was
raised that there's little point keeping it open?