Fixes KeyError when indexing request.META

[jmoldow]

Fixes KeyError when indexing request.META if 'wsgi.multiprocess' is not
present. This was a bug in DebugToolbar.should_render_panels().

Also adds test cases for DebugToolbar.should_render_panels().

[aaugustin]

PEP 3333 says:

In addition to the CGI-defined variables, the environ dictionary may also contain arbitrary operating-system "environment variables", and must contain the following WSGI-defined variables: (...) wsgi.multiprocess

If the variable isn't present, that's a bug in your WSGI server. What server are you using?

[jmoldow]

It is the server of a friend of mine, @uakfdotb, who was testing my pull request to upgrade our version of the debug toolbar [1]. I believe he was using some setup with Apache that did not include WSGI, though I don't know the details.

[1] learning-unlimited/ESP-Website#1034

[aaugustin]

Oh, right, Django 1.4 still supports mod_python :(

[aaugustin]

This should default to True in order to enable the safe but inefficient behavior on non-WSGI servers.

[aaugustin]

I appreciate the effort you put in writing the tests, but I'm not conviced they add that much value.

They're testing the implementation of should_render_panels. Any change in should_render_panels would result in a matching change in the tests. And they didn't catch the fact that your implementation returns the wrong value when wsgi.multiprocess isn't available...

[jmoldow]

I changed the default value.

test_should_render_panels_RENDER_PANELS_None_wsgi_multiprocess_None() does catch the problem, but it did not exist before we ran into the problem.

I can remove some of the other tests if you want.