Rewrote SDL sound synchronization, using a very old patch as a base for some of the changes

git-svn-id: https://svn.code.sf.net/p/vbam/code@1227 a31d4220-a93d-0410-bf67-fe4944624d44
SDL sound code now posts to semaphores no matter what, in case the other side is still waiting after a speedup transition

git-svn-id: https://svn.code.sf.net/p/vbam/code@1228 a31d4220-a93d-0410-bf67-fe4944624d44