Without this, the bots will download all resources for
every build. This consumes a lot of unnecessary traffic.
I tried experimenting with patterns ignoring everything
except the .sha1 files but wasn't able to get it working,
so this will have to do for now.
git-svn-id: http://webrtc.googlecode.com/svn/trunk@5082 4adac7df-926f-26a2-2b94-8c16560cd09d
