Sending HTML code as plain-text

Subscriptions.module is sending HTML code as plain-text. It needs to include Content-Type:text/html in the header. It also needs to seperate the From email address from the Headers in order to use the drupal_mail() function in Drupal 5.x.

This patch attempts to address both of these issues, but please review it for accuracy. I have not confirmed that this fixes the issue.