Send the post number to the template as it relates to it's position in the topic

The suggestion is to add a template variable in the postrow (POST_NUMBER) to send the number for each post as it relates to its position in the topic. For example, when someone opens a new topic, they will have post number 1, the second poster will have post number 2, and so on and so forth. This improvement would just send the data to the template, allowing the style author to decide whether or not to make use of it.