Prevent (Tile):has_base(), (Tile):has_road(), and (Tile):has_extra() lua script
functions to crash or produce error messages when the provided name doesn't
match any similar object of the ruleset.

Reported by Jeffrey C. Jacobs <timehorse>

See gna bug #22341

git-svn-id: svn://svn.gna.org/svn/freeciv/trunk@25707 a0f10bec-cc02-0410-94fc-a9cfff90b4cd
Move unit_tranported(pcargo) test from could_unit_load() to can_unit_load().
It was forbidding units to jump from a transport to another.

See gna bug #22380

git-svn-id: svn://svn.gna.org/svn/freeciv/trunk@25710 a0f10bec-cc02-0410-94fc-a9cfff90b4cd
Improved pf_reverse_map calculations.

See gna patch #4970

git-svn-id: svn://svn.gna.org/svn/freeciv/trunk@25713 a0f10bec-cc02-0410-94fc-a9cfff90b4cd
Make path-finding tools able to guess the real move rate of a unit type.

See gna patch #4971

git-svn-id: svn://svn.gna.org/svn/freeciv/trunk@25714 a0f10bec-cc02-0410-94fc-a9cfff90b4cd