t/t7505-prepare-commit-msg-hook.sh: use the $( ... ) construct for command substitution

The Git CodingGuidelines prefer the $(...) construct for command
substitution instead of using the backquotes `...`.

The backquoted form is the traditional method for command
substitution, and is supported by POSIX.  However, all but the
simplest uses become complicated quickly.  In particular, embedded
command substitutions and/or the use of double quotes require
careful escaping with the backslash character.

The patch was generated by:

for _f in $(find . -name "*.sh")
do
	perl -i -pe 'BEGIN{undef $/;} s/`(.+?)`/\$(\1)/smg'  "${_f}"
done

and then carefully proof-read.

Signed-off-by: Elia Pinto <gitter.spiros@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t7505-prepare-commit-msg-hook.sh

@@ -53,7 +53,7 @@ test_expect_success 'with hook (-m)' '
 	echo "more" >> file &&
 	git add file &&
 	git commit -m "more" &&
-	test "`git log -1 --pretty=format:%s`" = "message (no editor)"
+	test "$(git log -1 --pretty=format:%s)" = "message (no editor)"
 
 '
 
@@ -62,7 +62,7 @@ test_expect_success 'with hook (-m editor)' '
 	echo "more" >> file &&
 	git add file &&
 	GIT_EDITOR="\"\$FAKE_EDITOR\"" git commit -e -m "more more" &&
-	test "`git log -1 --pretty=format:%s`" = message
+	test "$(git log -1 --pretty=format:%s)" = message
 
 '
 
@@ -71,7 +71,7 @@ test_expect_success 'with hook (-t)' '
 	echo "more" >> file &&
 	git add file &&
 	git commit -t "$(git rev-parse --git-dir)/template" &&
-	test "`git log -1 --pretty=format:%s`" = template
+	test "$(git log -1 --pretty=format:%s)" = template
 
 '
 
@@ -80,7 +80,7 @@ test_expect_success 'with hook (-F)' '
 	echo "more" >> file &&
 	git add file &&
 	(echo more | git commit -F -) &&
-	test "`git log -1 --pretty=format:%s`" = "message (no editor)"
+	test "$(git log -1 --pretty=format:%s)" = "message (no editor)"
 
 '
 
@@ -89,17 +89,17 @@ test_expect_success 'with hook (-F editor)' '
 	echo "more" >> file &&
 	git add file &&
 	(echo more more | GIT_EDITOR="\"\$FAKE_EDITOR\"" git commit -e -F -) &&
-	test "`git log -1 --pretty=format:%s`" = message
+	test "$(git log -1 --pretty=format:%s)" = message
 
 '
 
 test_expect_success 'with hook (-C)' '
 
-	head=`git rev-parse HEAD` &&
+	head=$(git rev-parse HEAD) &&
 	echo "more" >> file &&
 	git add file &&
 	git commit -C $head &&
-	test "`git log -1 --pretty=format:%s`" = "$head (no editor)"
+	test "$(git log -1 --pretty=format:%s)" = "$head (no editor)"
 
 '
 
@@ -108,27 +108,27 @@ test_expect_success 'with hook (editor)' '
 	echo "more more" >> file &&
 	git add file &&
 	GIT_EDITOR="\"\$FAKE_EDITOR\"" git commit &&
-	test "`git log -1 --pretty=format:%s`" = default
+	test "$(git log -1 --pretty=format:%s)" = default
 
 '
 
 test_expect_success 'with hook (--amend)' '
 
-	head=`git rev-parse HEAD` &&
+	head=$(git rev-parse HEAD) &&
 	echo "more" >> file &&
 	git add file &&
 	GIT_EDITOR="\"\$FAKE_EDITOR\"" git commit --amend &&
-	test "`git log -1 --pretty=format:%s`" = "$head"
+	test "$(git log -1 --pretty=format:%s)" = "$head"
 
 '
 
 test_expect_success 'with hook (-c)' '
 
-	head=`git rev-parse HEAD` &&
+	head=$(git rev-parse HEAD) &&
 	echo "more" >> file &&
 	git add file &&
 	GIT_EDITOR="\"\$FAKE_EDITOR\"" git commit -c $head &&
-	test "`git log -1 --pretty=format:%s`" = "$head"
+	test "$(git log -1 --pretty=format:%s)" = "$head"
 
 '
 
@@ -141,7 +141,7 @@ test_expect_success 'with hook (merge)' '
 	git commit -m other &&
 	git checkout - &&
 	git merge --no-ff other &&
-	test "`git log -1 --pretty=format:%s`" = "merge (no editor)"
+	test "$(git log -1 --pretty=format:%s)" = "merge (no editor)"
 '
 
 test_expect_success 'with hook and editor (merge)' '
@@ -153,7 +153,7 @@ test_expect_success 'with hook and editor (merge)' '
 	git commit -m other &&
 	git checkout - &&
 	env GIT_EDITOR="\"\$FAKE_EDITOR\"" git merge --no-ff -e other &&
-	test "`git log -1 --pretty=format:%s`" = "merge"
+	test "$(git log -1 --pretty=format:%s)" = "merge"
 '
 
 cat > "$HOOK" <<'EOF'
@@ -164,7 +164,7 @@ EOF
 test_expect_success 'with failing hook' '
 
 	test_when_finished "git checkout -f master" &&
-	head=`git rev-parse HEAD` &&
+	head=$(git rev-parse HEAD) &&
 	echo "more" >> file &&
 	git add file &&
 	test_must_fail env GIT_EDITOR="\"\$FAKE_EDITOR\"" git commit -c $head
@@ -174,7 +174,7 @@ test_expect_success 'with failing hook' '
 test_expect_success 'with failing hook (--no-verify)' '
 
 	test_when_finished "git checkout -f master" &&
-	head=`git rev-parse HEAD` &&
+	head=$(git rev-parse HEAD) &&
 	echo "more" >> file &&
 	git add file &&
 	test_must_fail env GIT_EDITOR="\"\$FAKE_EDITOR\"" git commit --no-verify -c $head