Work around ash "alternate value" expansion bug

Ash (used as /bin/sh on many distros) has a shell expansion bug
for the form ${var:+word word}.  The result is a single argument
"word word".  Work around by using ${var:+word} ${var:+word} or
equivalent.

Signed-off-by: Ben Jackson <ben@ben.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-am.sh

@@ -571,7 +571,7 @@ do
 			GIT_COMMITTER_DATE="$GIT_AUTHOR_DATE"
 			export GIT_COMMITTER_DATE
 		fi &&
-		git commit-tree $tree ${parent:+-p $parent} <"$dotest/final-commit"
+		git commit-tree $tree ${parent:+-p} $parent <"$dotest/final-commit"
 	) &&
 	git update-ref -m "$GIT_REFLOG_ACTION: $FIRSTLINE" HEAD $commit $parent ||
 	stop_here $this

git-submodule.sh

@@ -204,8 +204,15 @@ cmd_add()
 	else
 
 		module_clone "$path" "$realrepo" || exit
-		(unset GIT_DIR; cd "$path" && git checkout -f -q ${branch:+-b "$branch" "origin/$branch"}) ||
-		die "Unable to checkout submodule '$path'"
+		(
+			unset GIT_DIR
+			cd "$path" &&
+			# ash fails to wordsplit ${branch:+-b "$branch"...}
+			case "$branch" in
+			'') git checkout -f -q ;;
+			?*) git checkout -f -q -b "$branch" "origin/$branch" ;;
+			esac
+		) || die "Unable to checkout submodule '$path'"
 	fi
 
 	git add "$path" ||

t/t7400-submodule-basic.sh

@@ -64,6 +64,16 @@ test_expect_success 'submodule add' '
 	)
 '
 
+test_expect_success 'submodule add --branch' '
+	(
+		cd addtest &&
+		git submodule add -b initial "$submodurl" submod-branch &&
+		git submodule init &&
+		cd submod-branch &&
+		git branch | grep initial
+	)
+'
+
 test_expect_success 'submodule add with ./ in path' '
 	(
 		cd addtest &&