HAMMER1 userspace on Linux

[Tomohiro Kusumi]

I've uploaded HAMMER1 userspace code which compiles on Linux distros.
https://github.com/kusumi/lh1

The fs itself doesn't exist on Linux, thus majority of commands that
require HAMMER1 ioctls are actually not usable.
In other words, newfs_hammer and hammer
blockmap/checkmap/show/show-undo/strip/recover commands are usable.
e.g. newfs_hammer'd image created on Linux is mountable on DragonFly.

Notes:
I haven't included mount_hammer at this point.
Dropped hammer "info" command.
Included DragonFly's fstyp which was originally ported from FreeBSD.

Further work on kernel side is not planned at the moment.