- Renamed private MediaManager::forceMediaRelease

- Renamed private MediaManager::forceMediaRelease
  function to forceReleaseShared (more exact name)
- Implemented forceRelaseAllMedia() that can be
  used to release also foreign (user) mounts.
- Added use of forceRelaseAllMedia for CD/DVDs
  if FORCE_RELEASE_FOREIGN is 1 (default 0)
- little cleanup of the checkAttached function