tests: use $TEST_DIRECTORY to refer to the t/ directory

Many test scripts assumed that they will start in a 'trash' subdirectory
that is a single level down from the t/ directory, and referred to their
test vector files by asking for files like "../t9999/expect".  This will
break if we move the 'trash' subdirectory elsewhere.

To solve this, we earlier introduced "$TEST_DIRECTORY" so that they can
refer to t/ directory reliably.  This finally makes all the tests use
it to refer to the outside environment.

With this patch, and a one-liner not included here (because it would
contradict with what Dscho really wants to do):

| diff --git a/t/test-lib.sh b/t/test-lib.sh
| index 70ea7e0..60e69e4 100644
| --- a/t/test-lib.sh
| +++ b/t/test-lib.sh
| @@ -485,7 +485,7 @@ fi
|  . ../GIT-BUILD-OPTIONS
|
|  # Test repository
| -test="trash directory"
| +test="trash directory/another level/yet another"
|  rm -fr "$test" || {
|         trap - exit
|         echo >&5 "FATAL: Cannot prepare test area"

all the tests still pass, but we would want extra sets of eyeballs on this
type of change to really make sure.

[jc: with help from Stephan Beyer on http-push tests I do not run myself;
 credits for locating silly quoting errors go to Olivier Marin.]

Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/t/t7500-commit.sh b/t/t7500-commit.sh
index 809bdba..7ae0bd0 100755
--- a/t/t7500-commit.sh
+++ b/t/t7500-commit.sh
@@ -46,15 +46,24 @@
 '
 
 test_expect_success 'a Signed-off-by line by itself should not commit' '
-	! GIT_EDITOR=../t7500/add-signed-off git commit --template "$TEMPLATE"
+	(
+		test_set_editor "$TEST_DIRECTORY"/t7500/add-signed-off &&
+		test_must_fail git commit --template "$TEMPLATE"
+	)
 '
 
 test_expect_success 'adding comments to a template should not commit' '
-	! GIT_EDITOR=../t7500/add-comments git commit --template "$TEMPLATE"
+	(
+		test_set_editor "$TEST_DIRECTORY"/t7500/add-comments &&
+		test_must_fail git commit --template "$TEMPLATE"
+	)
 '
 
 test_expect_success 'adding real content to a template should commit' '
-	GIT_EDITOR=../t7500/add-content git commit --template "$TEMPLATE" &&
+	(
+		test_set_editor "$TEST_DIRECTORY"/t7500/add-content &&
+		git commit --template "$TEMPLATE"
+	) &&
 	commit_msg_is "template linecommit message"
 '
 
@@ -62,7 +71,10 @@
 	echo "short template" > "$TEMPLATE" &&
 	echo "new content" >> foo &&
 	git add foo &&
-	GIT_EDITOR=../t7500/add-content git commit -t "$TEMPLATE" &&
+	(
+		test_set_editor "$TEST_DIRECTORY"/t7500/add-content &&
+		git commit -t "$TEMPLATE"
+	) &&
 	commit_msg_is "short templatecommit message"
 '
 
@@ -71,7 +83,10 @@
 	git config commit.template "$TEMPLATE" &&
 	echo "more content" >> foo &&
 	git add foo &&
-	GIT_EDITOR=../t7500/add-content git commit &&
+	(
+		test_set_editor "$TEST_DIRECTORY"/t7500/add-content &&
+		git commit
+	) &&
 	git config --unset commit.template &&
 	commit_msg_is "new templatecommit message"
 '
@@ -79,7 +94,7 @@
 test_expect_success 'explicit commit message should override template' '
 	echo "still more content" >> foo &&
 	git add foo &&
-	GIT_EDITOR=../t7500/add-content git commit --template "$TEMPLATE" \
+	GIT_EDITOR="$TEST_DIRECTORY"/t7500/add-content git commit --template "$TEMPLATE" \
 		-m "command line msg" &&
 	commit_msg_is "command line msg"
 '
@@ -88,8 +103,10 @@
 	echo "content galore" >> foo &&
 	git add foo &&
 	echo "standard input msg" |
-		GIT_EDITOR=../t7500/add-content git commit \
-			--template "$TEMPLATE" --file - &&
+	(
+		test_set_editor "$TEST_DIRECTORY"/t7500/add-content &&
+		git commit --template "$TEMPLATE" --file -
+	) &&
 	commit_msg_is "standard input msg"
 '
 
@@ -132,10 +149,12 @@
 
 test_expect_success '--signoff' '
 	echo "yet another content *narf*" >> foo &&
-	echo "zort" |
-		GIT_EDITOR=../t7500/add-content git commit -s -F - foo &&
+	echo "zort" | (
+		test_set_editor "$TEST_DIRECTORY"/t7500/add-content &&
+		git commit -s -F - foo
+	) &&
 	git cat-file commit HEAD | sed "1,/^$/d" > output &&
-	diff expect output
+	test_cmp expect output
 '
 
 test_expect_success 'commit message from file (1)' '