Start deprecating "git-command" in favor of "git command"

Start deprecating "git-command" in favor of "git command"

I realize that a lot of people use the "git-xyzzy" format, and we have
various historical reasons for it, but I also think that most people have
long since started thinking of the git command as a single command with
various subcommands, and we've long had the documentation talk about it
that way.

Slowly migrating away from the git-xyzzy format would allow us to
eventually no longer install hundreds of binaries (even if most of them
are symlinks or hardlinks) in users $PATH, and the _original_ reasons for
it (implementation issues and bash completion) are really long long gone.

Using "git xyzzy" also has some fundamental advantages, like the ability
to specify things like paging ("git -p xyzzy") and making the whole notion
of aliases act like other git commands (which they already do, but they do
*not* have a "git-xyzzy" form!)

Anyway, while actually removing the "git-xyzzy" things is not practical
right now, we can certainly start slowly to deprecate it internally inside
git itself - in the shell scripts we use, and the test vectors.

This patch adds a "remove-dashes" makefile target, which does that. It
isn't particularly efficient or smart, but it *does* successfully rewrite
a lot of our shell scripts to use the "git xyzzy" form for all built-in
commands.

(For non-builtins, the "git xyzzy" format implies an extra execve(), so
this script leaves those alone).

So apply this patch, and then run

	make remove-dashes
	make test
	git commit -a

to generate a much larger patch that actually starts this transformation.

(The only half-way subtle thing about this is that it also fixes up
git-filter-branch.sh for the new world order by adding quoting around
the use of "git-commit-tree" as an argument. It doesn't need it in that
format, but when changed into "git commit-tree" it is no longer a single
word, and the quoting maintains the old behaviour).

NOTE! This does not yet mean that you can actually stop installing the
"git-xyzzy" binaries for the builtins. There are some remaining places
that want to use the old form, this just removes the most obvious ones
that can easily be done automatically.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>