Pathfinding unknown movement cost is more ruleset-flexible:
* The cost is equal to the highest movement cost the unit can encounter.
* A malus (mutliplied by 2) is applied if a unit cannot enter all terrains.
* UTYF_IGTER is now handled.
* The value is now cached by unit type.

Patch by Emmet Hikory (persia@gna) and me

See patch #3903

git-svn-id: svn://svn.gna.org/svn/freeciv/trunk@24335 a0f10bec-cc02-0410-94fc-a9cfff90b4cd
Refactored backtrace printing code so that there's now backtrace_print() function available
for callers outside of the logging code.

See patch #4463


git-svn-id: svn://svn.gna.org/svn/freeciv/trunk@24336 a0f10bec-cc02-0410-94fc-a9cfff90b4cd
Replace all "sellect" words in sdl2-client code with respective "select" word.

See patch #4464


git-svn-id: svn://svn.gna.org/svn/freeciv/trunk@24337 a0f10bec-cc02-0410-94fc-a9cfff90b4cd