Another travis script fix

I spent hours debugging an annoying keychain problem, which turned out to be a default timeout of 5 minutes set by default on the use of the keychain.
See http://www.egeek.me/2013/02/23/jenkins-and-xcode-user-interaction-is-not-allowed/ for more info.

Also added comments to the script to increase readability.
I'm not sure if this line adds anything?