Adding the option to build ideviceinstaller from HEAD

The libimobiledevice formula has been bumped to version 1.1.5. This version has breaking changes for ideviceinstaller 1.0.1. A fix has been committed for [ideviceinstaller]( http://cgit.sukimashita.com/ideviceinstaller.git/commit/?id=78238523bc5aff1d699a202e82dea1f02e780fb8), but the only way to install it via homebrew is to support installing with `--HEAD`. I've tested this with OSX 10.8.3.