git-submodule.sh: improve parsing of some long options

Some command-line options have a long form which takes an argument. In
this case, the argument can be given right after `='; for example,
"--depth" takes a numerical argument, which can be given as "--depth=X".

Support the case where the argument is given right after `=' for all
long options, in order to improve consistency throughout the script.

Signed-off-by: Roy Eldar <royeldar0@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-submodule.sh

@@ -77,6 +77,9 @@ cmd_add()
 			branch=$2
 			shift
 			;;
+		--branch=*)
+			branch="${1#--branch=}"
+			;;
 		-f | --force)
 			force=$1
 			;;
@@ -110,6 +113,9 @@ cmd_add()
 			custom_name=$2
 			shift
 			;;
+		--name=*)
+			custom_name="${1#--name=}"
+			;;
 		--depth)
 			case "$2" in '') usage ;; esac
 			depth="--depth=$2"
@@ -425,6 +431,9 @@ cmd_set_branch() {
 			branch=$2
 			shift
 			;;
+		--branch=*)
+			branch="${1#--branch=}"
+			;;
 		--)
 			shift
 			break