misc tweaks

Hi!

First of all, nice app! I like it's size.

There are, however, a couple of nits:

First and foremost, many of my mail-attachments are text/x-patch or text/x-diff, some are even application/octet-stream depending on the MUA deciding how to obfuscate the attached patches.
To be able to read them, i need an app that registers for all these mimeTypes. That patch in this series is the most important for me. I would be grateful if you would consider applying at least this one.

The other stuff fell out while i tried to rebuild your Text Viewer :)
Thanks alot in advance for your time!
Cheers,