completion: add remaining flags to checkout

In the commits 1fc458d9 (builtin/checkout: add --recurse-submodules
switch, 2017-03-14), 08d595dc (checkout: add --ignore-skip-worktree-bits
in sparse checkout mode, 2013-04-13) and 32669671 (checkout: introduce
--detach synonym for "git checkout foo^{commit}", 2011-02-08) checkout
gained new flags but the completion was not updated, although these flags
are useful completions. Add them.

The flags --force and --ignore-other-worktrees are not added as they are
potentially dangerous.

The flags --progress and --no-progress are only useful for scripting and are
therefore also not included.

Signed-off-by: Thomas Braun <thomas.braun@virtuell-zuhause.de>
Reviewed-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/completion/git-completion.bash

@@ -1250,7 +1250,8 @@ _git_checkout ()
 	--*)
 		__gitcomp "
 			--quiet --ours --theirs --track --no-track --merge
-			--conflict= --orphan --patch
+			--conflict= --orphan --patch --detach --ignore-skip-worktree-bits
+			--recurse-submodules --no-recurse-submodules
 			"
 		;;
 	*)

t/t9902-completion.sh

@@ -1245,6 +1245,10 @@ test_expect_success 'double dash "git checkout"' '
 	--conflict=
 	--orphan Z
 	--patch Z
+	--detach Z
+	--ignore-skip-worktree-bits Z
+	--recurse-submodules Z
+	--no-recurse-submodules Z
 	EOF
 '