Made internal references in gui-sdl2 theme to point files in the same theme and not gui-sdl theme.

See bug #22370


git-svn-id: svn://svn.gna.org/svn/freeciv/trunk@25726 a0f10bec-cc02-0410-94fc-a9cfff90b4cd
Share the code adding the success probability to a spy actions button text

Bonus: the Xaw client will now display a spy actions success probability

See patch #4980

git-svn-id: svn://svn.gna.org/svn/freeciv/trunk@25727 a0f10bec-cc02-0410-94fc-a9cfff90b4cd