Document uWSGI requirements

[dstufft]

Just adding this here as a note since I think it should be documented and I don't want to have it get lost.

Essentially, if you try to use uWSGI + pyramid_debugtoolbar it's going to fail by default with a KeyError: PATH_INFO. This is because, by default, uWSGI attempts to reduce the number of mallocs it takes to serve a request and it will instead preallocate a Python dictionary, then for each request it will populate that dictionary, call the WSGI callable, and then afterwords it will clear that dictionary. However, things like pyramid_debugtoolbar expect to be able to keep a reference to the environ dictionary and use that after the request has finished. Once you know the issue is a issue, fixing it is pretty trivial, uWSGI allows you to configure this behavior and go to a more typical "allocate a dictionary per request, let the GC handle cleaning it up" behavior using the --wsgi-env-behavior holy configuration option.

[stevepiercy]

Suggest a sub-section under Setup, maybe "Setup with uWSGI servers"?

[habnabit]

wow! that exactly explains the weird behavior I was having. maybe debugtoolbar could copy those lists itself anyway?