Show X-UserAgent and/or X-Mailer in the fancy header.
I sorta like it, although it does take up space.
Yes, we could add a config option... but who wants yet-another-config-option?

What do others think about it?
For now, I will keep this only in pim+ branch. I won't move it into the 3.5 branch or trunk unless I get a resounding "Yes we want this" from testers and core devs.

This patch provided by Fram Thieme.