Updates and fixes

* Update to iOS 8.1 / OS X 10.10
* Update to the GStreamer 1.4 stable branch to get some newer backported patches
* Follow redirects when downloading icu (it looks like they moved their downloads to sourceforge or something)
This means that we can *only* build with the 10.10 SDK now, right? Meaning that everybody will have to upgrade.
Maybe checking for both directories like it's done for the iOS SDKs would be better