delete old builds

[abma]

old builds should be deleted as they use A LOT of disk space.

i.e.: http://evo.repo.springrts.com/builds/ & http://zk.repo.springrts.com/builds/

imo keep 5 of the most recent builds:

http://stackoverflow.com/questions/2960022/shell-script-to-count-files-then-remove-oldest-files