Don't start playing a SoundEffectInstance all over again if it's already playing
Fixed PlayPosition on Windows 8
Fixed render targets on WP8
Since the MonoTouch bug was fixed with the sensor events, we can revert to using their data
Merge branch 'develop3d' of https://github.com/mono/MonoGame into w8_play
Reapply
Merge pull request #1330 from Nezz/w8_playposition

Fixed PlayPosition on Windows 8
Merge pull request #1328 from Nezz/w8_play

SoundEffectInstance play bugfix
Merge pull request #1333 from Nezz/ios_sensors

Use sensor data on iOS
Merge pull request #1331 from Nezz/wp8_rendertarget

Fixed render targets on WP8
Merge pull request #20 from mono/develop3d

Merge back from develop3d