hooks/post-receive-email: use plumbing instead of git log/show

This way the hook doesn't have to keep being tweaked as porcelain
learns new features like color and pagination.

While at it, replace the "git rev-list | git shortlog" idiom with
plain "git shortlog" for simplicity.

Except for depending less on the value of settings like '[log]
abbrevCommit', no change in output intended.

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/hooks/post-receive-email

@@ -471,7 +471,7 @@ generate_delete_branch_email()
 	echo "       was  $oldrev"
 	echo ""
 	echo $LOGBEGIN
-	git show -s --pretty=oneline $oldrev
+	git diff-tree -s --always --pretty=oneline $oldrev
 	echo $LOGEND
 }
 
@@ -547,11 +547,11 @@ generate_atag_email()
 		# performed on them
 		if [ -n "$prevtag" ]; then
 			# Show changes since the previous release
-			git rev-list --pretty=short "$prevtag..$newrev" | git shortlog
+			git shortlog "$prevtag..$newrev"
 		else
 			# No previous tag, show all the changes since time
 			# began
-			git rev-list --pretty=short $newrev | git shortlog
+			git shortlog $newrev
 		fi
 		;;
 	*)
@@ -571,7 +571,7 @@ generate_delete_atag_email()
 	echo "       was  $oldrev"
 	echo ""
 	echo $LOGBEGIN
-	git show -s --pretty=oneline $oldrev
+	git diff-tree -s --always --pretty=oneline $oldrev
 	echo $LOGEND
 }
 
@@ -617,7 +617,7 @@ generate_general_email()
 	echo ""
 	if [ "$newrev_type" = "commit" ]; then
 		echo $LOGBEGIN
-		git show --no-color --root -s --pretty=medium $newrev
+		git diff-tree -s --always --pretty=medium $newrev
 		echo $LOGEND
 	else
 		# What can we do here?  The tag marks an object that is not
@@ -636,7 +636,7 @@ generate_delete_general_email()
 	echo "       was  $oldrev"
 	echo ""
 	echo $LOGBEGIN
-	git show -s --pretty=oneline $oldrev
+	git diff-tree -s --always --pretty=oneline $oldrev
 	echo $LOGEND
 }