Prevent cross posting from reverting issue information

If two users are adding a comment to an issue at the same time and the first posted comment changes the issue information, when the second comment gets posted, the issue information will be reverted because the second commentator still has the original issue information in their form submission.

Got bit by this twice today. And its only 9am. As more and more people post to d.o, this will become a much more frequent problem.

I envision a fix for this by using some hidden fields that hold the original values. That way the backend PHP can compare the original to the "new" value and if no changes are made, those fields won't be updated when posting the comment.

Also, when previewing a comment, any field that has no changes should be updated to reflect any changes that were made since the user first started typing the comment.