[Libguestfs] PATCH: Allow specifying the filesystem driver for guestmount

[Dave Vasilevsky]

Thanks for investigating! Hopefully the protocol compatibility can be
documented--it would be good to know in other situations where one is
forced to use a fixed appliance, like on BSD and OS X.

There's one more little thing that came up. You recommended in IRC
that for testing I do "LIBGUESTFS_PATH=/path/to/appliance ./run
./fish/guestfish ...". But it turns out that the ./run script
unconditionally overwrites LIBGUESTFS_PATH, preferring the local
"appliance" directory. This was easy to work around, but I thought you
should be aware of it, in case it's not the intended behaviour.

This crazy project does seem to be working, and I now have write
access to journaled HFS+ from Linux! I'll write some documentation for
others who want to try it, and of course libguestfs will feature
prominently.

Dave