[PATCH] git-submodule.sh: Support 'checkout' as a valid update command

[Francesco Pretto <ceztko@gmail.com>]

According to "Documentation/gitmodules.txt", 'checkout' is a valid
'submodule.<name>.update' command. Also "git-submodule.sh" refers to
it and processes it correctly. Reflecting commit 'ac1fbb' to support
this syntax and also validate property values during 'update' command,
issuing an error if the value found is unknown.

Signed-off-by: Francesco Pretto <ceztko@gmail.com>
---
 git-submodule.sh | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/git-submodule.sh b/git-submodule.sh
index 2677f2e..4a30087 100755
--- a/git-submodule.sh
+++ b/git-submodule.sh
@@ -622,7 +622,7 @@ cmd_init()
 		   test -z "$(git config submodule."$name".update)"
 		then
 			case "$upd" in
-			rebase | merge | none)
+			checkout | rebase | merge | none)
 				;; # known modes of updating
 			*)
 				echo >&2 "warning: unknown update mode '$upd' suggested for submodule '$name'"
@@ -805,6 +805,17 @@ cmd_update()
 			update_module=$update
 		else
 			update_module=$(git config submodule."$name".update)
+			case "$update_module" in
+			'')
+				;; # Unset update mode
+			checkout | rebase | merge | none)
+				;; # Known update modes
+			!*)
+				;; # Custom update command
+			*)
+				die "$(eval_gettext "Invalid update mode '$update_module' for submodule '$name'")"
+				;;
+			esac
 		fi
 
 		displaypath=$(relative_path "$prefix$sm_path")
-- 
1.8.5.2.229.g4448466.dirty