Added rewind feature. Currently only supported via GTK and needs SHM. Rewind save state depth is configured via RewindCount config param. Recommended value is 200 or so -> uses less than 1G of memory

git-svn-id: https://pcsxr.svn.codeplex.com/svn/pcsxr@88433 e17a0e51-4ae3-4d35-97c3-1a29b211df97