Add instructions to install libjpeg-dev or equivalent to docs

[Christopher Allan Webber]

People are constantly running into this irritation because a custom PIL gets built in their virtualenv:

IOError: decoder jpeg not available

Should be easy to do. Add both to the sphinx docs in the mediagoblin/ checkout and to the wiki ​Hacking Howto

[Dani Estevez]

I tried many things to fix this issue, being these the most important:

• sudo apt-get install zlib1g-dev libjpeg8-dev libpng-dev
• sudo apt-get build-dep python-imaging
• sudo pip install pillow pillow seemed to be the key
• Create symlinks (for Natty problem suggested in ​http://ubuntuforums.org/showthread.php?t=1751455&page=2)

[Jakob Kramer]

I think it is enough to say: “Make sure there is no custom PIL in your lib folder.” My problems have always been solved by that (and only that). I think we should replace the suggestion to install pillow with making sure that there is no custom PIL and then close the issue.

I doubt installing pillow helps…

[Jakob Kramer]

Can be closed, because PIL is not being installed by setup.py anymore.