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.
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.