Implement TH_ENCCTL_SET_SPLEVEL and TH_ENCCTL_GET_SPLEVEL_MAX.

0: Same as quick_p = 0 (exhaustive motion search)
1: Same as quick_p = 1 (default, combination of quick and exhaustive motion search)
2: No motion compensation at all. Very fast but impacts negatively on both image quality and bitrate. Perhaps useful for e.g. videoconferencing (little motion) on slow systems. Definately of limited use.

svn path=/trunk/theora/; revision=13368