completion: add missing git-rebase options

This adds the --no-* variants where those are documented in
git-rebase(1).

Signed-off-by: John Keeping <john@keeping.me.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/completion/git-completion.bash

@@ -1687,8 +1687,12 @@ _git_rebase ()
 			--preserve-merges --stat --no-stat
 			--committer-date-is-author-date --ignore-date
 			--ignore-whitespace --whitespace=
-			--autosquash --fork-point --no-fork-point
-			--autostash
+			--autosquash --no-autosquash
+			--fork-point --no-fork-point
+			--autostash --no-autostash
+			--verify --no-verify
+			--keep-empty --root --force-rebase --no-ff
+			--exec
 			"
 
 		return