add wsgi_intercept.STRICT_RESPONSE_HEADERS as a flag

[cdent]

Add a flag to build_tests that allows turning wsgi_intercept.STRICT_RESPONSE_HEADERS on and in the wsgi intercept context manager fixture.

The challenge here is getting the flag value to the fixture.

Also the number of parameters on build_tests is getting absurd. It's time to explore some new models.

/cc @jd

[jd]

What struck me when I took a look at that, is more the global variable that is provided by wsgi_intercept. That might be the first thing to change.

[cdent]

@FND and I talked about that in IRC some time last week and it was basically what I said to you: The use of a global is because of the multiple entry points into wsgi-intercept's big mess, which will be a large effort to fix.

We can hide that complexity in gabbi (without regard to the implementation being what it is now or how it changes later) now, with something like this flag.