Install afsd.fuse and man page if built

Install afsd.fuse and man page if built

If --enable-fuse-client is passed to configure and afsd.fuse is built,
install it into the same directory as afsd and install afsd.fuse.8 as a
symlink to the afsd.8 man page.  Add documentation of afsd.fuse to the
afsd man page.

Change-Id: I7d0cd3992a8466e626af2191c713e5623cc40d84
Reviewed-on: http://gerrit.openafs.org/1792
Tested-by: Russ Allbery <rra@stanford.edu>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>