move git mirror from wesnoth.in to build.wesnoth.in

[excavador]

1. Move wesnoth.in:/root/battle-for-wesnoth-svn from wesnoth.in to build.wesnoth.in:/home/git/
2. Move update scripts wesnoth.in:/root/battle-for-wesnoth-svn/[run_]update.sh to build.wesnoth.in:/home/git/battle-for-wesnoth-svn
3. Add task to cron