cmd/fuse: tweak the wording of the import guard error message

cmd/fuse: tweak the wording of the import guard error message

"python-fuse" is not quite correct, since this is confusingly what Debian calls
(in order to conform to Debian Python package naming policy) the upstream
package actually called "fuse-python". Other distros do refer to the package as
fuse-python.

Tweak the wording slightly in order to avoid this ambiguity, and also to make it
congruous to the wording of a similar import guard I used in cmd/web.

Signed-off-by: Robert S. Edmonds <edmonds@debian.org>