Bug 904918: Odin Float32 support; p=bbouvier,dougc r=luke,sstangl

Authors:
- Douglas Crosher (dougc) for the ARM backend support
- Benjamin Bouvier (bbouvier) for everything else
Bug 904918: Odin Float32 support: tests; r=luke
Bug 949474 - Reflect the fact that the nominal range for the sampleRate argument of the AudioContext.createBuffer changed in the spec. r=ehsan