declare wsession files that are fallback session with IsFallbackSession key, that is now handled by the waylandloginmanager

git-svn-id: https://rebeccablackos.svn.sourceforge.net/svnroot/rebeccablackos@2777 56e3d1a8-0179-4092-b3e2-9fbbcda0c0a9
waylandloginmanager: correctly assume wsession files that do not specify if they support a backend, that it is NOT supported, and try to guess the next one that it supports. 

git-svn-id: https://rebeccablackos.svn.sourceforge.net/svnroot/rebeccablackos@2778 56e3d1a8-0179-4092-b3e2-9fbbcda0c0a9