git-quiltimport /bin/sh-ism fix

Bryan Wu reported
/usr/local/bin/git-quiltimport: 114: Syntax error: Missing '))'

Most bourne-ish shells I have here accept
 x=$((echo x)|cat)
but all bourne-ish shells I have here accept
 x=$( (echo x)|cat)
because $(( might mean arithmetic expansion.
Signed-off-by: NFrancis Daly <francis@daoine.org>
Signed-off-by: NJunio C Hamano <junkio@cox.net>

git-quiltimport.sh

@@ -115,7 +115,7 @@ for patch_name in $(cat "$QUILT_PATCHES/series" | grep -v '^#'); do
 	if [ -z "$dry_run" ] ; then
 		git-apply --index -C1 "$tmp_patch" &&
 		tree=$(git-write-tree) &&
-		commit=$((echo "$SUBJECT"; echo; cat "$tmp_msg") | git-commit-tree $tree -p $commit) &&
+		commit=$( (echo "$SUBJECT"; echo; cat "$tmp_msg") | git-commit-tree $tree -p $commit) &&
 		git-update-ref -m "quiltimport: $patch_name" HEAD $commit || exit 4
 	fi
 done