Cython and Python versions of CIMultiDict treat key case differently about multidict

[mikenerone]

Having thought about it, I'm more on the fence about which behavior is more correct. The title-style output makes sense for HTTP headers. :/

[asvetlov]

In this case Cython version is correct, pure Python should be fixed

[mikenerone]

Cool, I'll be happy to make a PR if you like. I can be a contributor for just deleting one line. :P

Well, I suppose I'd provide a test or two, as well.

[asvetlov]

Please do.
Thank you for report

[webknjaz]

I can be a contributor for just deleting one line.

One line and a test, please:)

[mikenerone]

I noticed the same effect in the Python implementation in several of the places where a KeyError is raised, where the error message includes the title-ized key instead of the key passed by the caller (again, unlike the Cython implementations, which handle this correctly). As it's basically the same logic error, would you like me to fix these in the same PR or make a separate one?

[asvetlov]

Yes, casing should be preserved as Cython version does.