Restored "SDL.h" include to client gui source files containing main(), so
main() gets renamed by the macro in that header.
Added comments explaining why it's needed there despite no obvious dependencies.

See patch #4448


git-svn-id: svn://svn.gna.org/svn/freeciv/trunk@24242 a0f10bec-cc02-0410-94fc-a9cfff90b4cd
Fixed find_next_free_port() to return the actual free port found, and to check
port from specific interface. This fixes the problems of client to fork a server
and connect to it when there's already another such server running.

Reported by myself and Christian Knoke <chrisk>

See bug #19720


git-svn-id: svn://svn.gna.org/svn/freeciv/trunk@24244 a0f10bec-cc02-0410-94fc-a9cfff90b4cd
Always unref pixmaps got from sprite_get_pixbuf()

See bug #21534


git-svn-id: svn://svn.gna.org/svn/freeciv/trunk@24247 a0f10bec-cc02-0410-94fc-a9cfff90b4cd
Fixed gettext warnings.

See bug #21521


git-svn-id: svn://svn.gna.org/svn/freeciv/trunk@24250 a0f10bec-cc02-0410-94fc-a9cfff90b4cd