Bug 945419 - Use upstream opus git version format. r=derf

We only want tags which match the release naming convention,
and --dirty is very important for catching local changes.
Bug 945419 - Fix fixed-point opus stereo encode regression. r=jmspeex.
Bug 945419 - Update libopus to 1.1 final. r=cpearce

The code change only affects the opus custom modes which we do
not use, so this commit effectively just changes the version number.