libdvdread patch for command mneumonics

Hi, I know you guys know how to decode the DVD VM command set, but it'd
be really nice if you'd include that in libdvdread, since it can already
decode everything else.

Also, it'd be nice to have a utility to dump the VOB NAV packets.

I've included a patch that does both -- note that the vob_dump utility
is pretty poor since it doesn't use the actual libdvdread routines to
open and read the VOB file (just to print the output).

Should ifo_dump be removed from ogle, since it's really more of a
libdvdread type application (and the code is duplicated there anyways?) 
It would be nice if 'make install' would install ifo_dump and the
assorted utilites from libdvdread instead of me having to copy them out
myself.

Anyways, here's the patch, hope it's useful.