Use present = FALSE requirements instead of nreqs vector in classic ruleset
effects.ruleset.

See patch #4411


git-svn-id: svn://svn.gna.org/svn/freeciv/trunk@24755 a0f10bec-cc02-0410-94fc-a9cfff90b4cd
Addede support for baseURL that's relative to the URL of the .modpack itself.

See patch #4618


git-svn-id: svn://svn.gna.org/svn/freeciv/trunk@24756 a0f10bec-cc02-0410-94fc-a9cfff90b4cd