Do not rely on the exit status of "unset" for unset variables

POSIX says that exit status "0" means that "unset" successfully unset
the variable.  However, it is kind of ambiguous if an environment
variable which was not set could be successfully unset.

At least the default shell on HP-UX insists on reporting an error in
such a case, so just ignore the exit status of "unset".

[Dscho: extended the patch to git-submodule.sh, as Junio realized that
 this is the only other place where we check the exit status of "unset".]

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-submodule.sh

@@ -158,7 +158,7 @@ module_add()
 	die "'$path' already exists in the index"
 
 	module_clone "$path" "$realrepo" || exit
-	(unset GIT_DIR && cd "$path" && git checkout -q ${branch:+-b "$branch" "origin/$branch"}) ||
+	(unset GIT_DIR; cd "$path" && git checkout -q ${branch:+-b "$branch" "origin/$branch"}) ||
 	die "Unable to checkout submodule '$path'"
 	git add "$path" ||
 	die "Failed to add submodule '$path'"
@@ -228,14 +228,14 @@ modules_update()
 			module_clone "$path" "$url" || exit
 			subsha1=
 		else
-			subsha1=$(unset GIT_DIR && cd "$path" &&
+			subsha1=$(unset GIT_DIR; cd "$path" &&
 				git rev-parse --verify HEAD) ||
 			die "Unable to find current revision in submodule path '$path'"
 		fi
 
 		if test "$subsha1" != "$sha1"
 		then
-			(unset GIT_DIR && cd "$path" && git-fetch &&
+			(unset GIT_DIR; cd "$path" && git-fetch &&
 				git-checkout -q "$sha1") ||
 			die "Unable to checkout '$sha1' in submodule path '$path'"
 
@@ -246,7 +246,7 @@ modules_update()
 
 set_name_rev () {
 	revname=$( (
-		unset GIT_DIR &&
+		unset GIT_DIR
 		cd "$1" && {
 			git describe "$2" 2>/dev/null ||
 			git describe --tags "$2" 2>/dev/null ||
@@ -285,7 +285,7 @@ modules_list()
 		else
 			if test -z "$cached"
 			then
-				sha1=$(unset GIT_DIR && cd "$path" && git rev-parse --verify HEAD)
+				sha1=$(unset GIT_DIR; cd "$path" && git rev-parse --verify HEAD)
 				set_name_rev "$path" "$sha1"
 			fi
 			say "+$sha1 $path$revname"

t/t0001-init.sh

@@ -25,7 +25,7 @@ check_config () {
 
 test_expect_success 'plain' '
 	(
-		unset GIT_DIR GIT_WORK_TREE &&
+		unset GIT_DIR GIT_WORK_TREE
 		mkdir plain &&
 		cd plain &&
 		git init
@@ -35,7 +35,7 @@ test_expect_success 'plain' '
 
 test_expect_success 'plain with GIT_WORK_TREE' '
 	if (
-		unset GIT_DIR &&
+		unset GIT_DIR
 		mkdir plain-wt &&
 		cd plain-wt &&
 		GIT_WORK_TREE=$(pwd) git init
@@ -48,7 +48,7 @@ test_expect_success 'plain with GIT_WORK_TREE' '
 
 test_expect_success 'plain bare' '
 	(
-		unset GIT_DIR GIT_WORK_TREE GIT_CONFIG &&
+		unset GIT_DIR GIT_WORK_TREE GIT_CONFIG
 		mkdir plain-bare-1 &&
 		cd plain-bare-1 &&
 		git --bare init
@@ -58,7 +58,7 @@ test_expect_success 'plain bare' '
 
 test_expect_success 'plain bare with GIT_WORK_TREE' '
 	if (
-		unset GIT_DIR GIT_CONFIG &&
+		unset GIT_DIR GIT_CONFIG
 		mkdir plain-bare-2 &&
 		cd plain-bare-2 &&
 		GIT_WORK_TREE=$(pwd) git --bare init
@@ -72,7 +72,7 @@ test_expect_success 'plain bare with GIT_WORK_TREE' '
 test_expect_success 'GIT_DIR bare' '
 
 	(
-		unset GIT_CONFIG &&
+		unset GIT_CONFIG
 		mkdir git-dir-bare.git &&
 		GIT_DIR=git-dir-bare.git git init
 	) &&
@@ -82,7 +82,7 @@ test_expect_success 'GIT_DIR bare' '
 test_expect_success 'GIT_DIR non-bare' '
 
 	(
-		unset GIT_CONFIG &&
+		unset GIT_CONFIG
 		mkdir non-bare &&
 		cd non-bare &&
 		GIT_DIR=.git git init
@@ -93,7 +93,7 @@ test_expect_success 'GIT_DIR non-bare' '
 test_expect_success 'GIT_DIR & GIT_WORK_TREE (1)' '
 
 	(
-		unset GIT_CONFIG &&
+		unset GIT_CONFIG
 		mkdir git-dir-wt-1.git &&
 		GIT_WORK_TREE=$(pwd) GIT_DIR=git-dir-wt-1.git git init
 	) &&
@@ -103,7 +103,7 @@ test_expect_success 'GIT_DIR & GIT_WORK_TREE (1)' '
 test_expect_success 'GIT_DIR & GIT_WORK_TREE (2)' '
 
 	if (
-		unset GIT_CONFIG &&
+		unset GIT_CONFIG
 		mkdir git-dir-wt-2.git &&
 		GIT_WORK_TREE=$(pwd) GIT_DIR=git-dir-wt-2.git git --bare init
 	)