bash: Classify cat-file and reflog as plumbing.

bash: Classify cat-file and reflog as plumbing.

Now that git-show is capable of displaying any file content from any
revision and is the approved Porcelain-ish level method of doing so,
cat-file should no longer be classified as a user-level utility by
the bash completion package.

I'm also classifying the new git-reflog command as plumbing for the
time being as there are no subcommands which are really useful to
the end-user.  git-gc already invokes `git reflog expire --all`,
which makes it rather unnecessary for the user to invoke it directly.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>