Initial import of character device in userspace support for FreeBSD.
The CUSE library is a wrapper for the devfs kernel functionality which
is exposed through /dev/cuse . In order to function the CUSE kernel
code must either be enabled in the kernel configuration file or loaded
separately as a module. Currently none of the committed items are
connected to the default builds, except for installing the needed
header files. The CUSE code will be connected to the default world and
kernel builds in a follow-up commit.

The CUSE module was written by Hans Petter Selasky, somewhat inspired
by similar functionality found in FUSE. The CUSE library can be used
for many purposes. Currently CUSE is used when running Linux kernel
drivers in user-space, which need to create a character device node to
communicate with its applications. CUSE has full support for almost
all devfs functionality found in the kernel:
 - kevents
 - read
 - write
 - ioctl
 - poll
 - open
 - close
 - mmap
 - private per file handle data

Requested by several people. Also see "multimedia/cuse4bsd-kmod" in
ports.