This is a fix for #1280. Added lock around the access to the sound effect management lists. Also changed the use of HashSet in lieu of List.
Song.Duration property implementation fix

Android and Linux Song class implementation to support Duration (read
the duration from .xnb file while loading the song)
Merge pull request #1290 from aghajani/skywave_song_2

Song.Duration property implementation fix
Ouya: Correct Y direction of axis
Merge branch 'develop3d' of https://github.com/mono/MonoGame into pull1291
Resuming a paused sound was not working correctly
due to a guard in Play that prevented the same instance being played twice.
Now also protects against Resume and Pause being called many times.
Fixes issue #1263.
Merge pull request #1292 from slygamer/issue1263

Resuming a paused sound was not working correctly
Merge pull request #1282 from totallyeviljake/ISSUE_1280_R1

This is a fix for #1280. Added lock around access to management lists.
First run PVRTC Support for the pipeline.
Changed function name in PVRTexLibC. Added configuration for x64.
Added PVRTCBitmapContent.
Merge branch 'develop3d' into FontProcessor
PVRTCBitmapContent is no longer a public class.
Updating submodule reference.
Deleting old .dll's from Tools folder, as they've been moved into ThirdParty/Libs.
Merge pull request #1301 from SickheadGames/FontProcessor

PVRTC support added to pipeline.