Moving util.dict_to_tuple_key() into only module that uses it.

[dhermes]

When I filed #428 I compared the modules to see what was superfluous and noticed that this method only had one user. This change may not be "allowed" since it removes a public interface.

[dhermes]

For some reason this didn't trigger the Travis hook?

[dhermes]

@nathanielmanistaatgoogle Don't forget to weigh in on whether or not moving this is allowed (since it is a public interface)

[nathanielmanistaatgoogle]

I endorse this change, despite it technically regressing the public interface of the library. The code element being withdrawn has nothing to do with authentication or cryptography or security or anything else that is part of the intended surface area of the library.

I was actually just the other day defending another library's many many underscores and highly restricted public interface and I think this a good example of what I was describing in that conversation about how too often things are accidentally public because underscores are cosmetically unattractive and library authors are slow to adopt a habit of "everything hidden by default when first written and then public only after thoughtful consideration that it needs to be public to serve the library's users". :-)

[dhermes]

I am a big fan of that approach.

I addressed the review comments. PTAL.

[dhermes]

And we even got Travis to fire on the new commit!

[nathanielmanistaatgoogle]

Looks great; squash, wait a reasonable time for test results (it is Saturday after all), and merge. :-)