Apparently the keychain re-locks fairly rapidly, so run the unlock script
right before running the packaging script. This is non-portable to another Mac slave, but will do for now.
Note this is currently hard-coding a source path for rsync which only works on my machine - which is the Mac jenkins slave. This will be updated shortly.
Capture most of the build logic in a script (ie. visible to Git, and outside Jenkins). use XCodebuild to run the actual compiles, so we get Clang. Use the Xcode 4.3 SDK paths.
