Various compat changes for recent rusts

[kentfredric]

I'm aware that this is officially deprecated.

This set of changes is prompted by having things that continue to require rustc-serialize in some capacity, and the desire as a vendor to ensure that rustc-serialize thus continues to be usable.

Fixing the tests is required to help us ensure it continues to be usable, because tests help identify when a mechanism breaks.

Alas, due to the derive macro's no longer seeming to exist, I've had to exorcise all tests that relied on those macros.

Some of these changes are also spurred on by the lib.rs explicit statement:

![cfg_attr(test, deny(warnings))]

Which for whatever reason doesn't adequately respond to --cap-lints warn.

If this change set is not valuable, or at least, if not all changes are deemed valuable, this PR may still be helpful for other linux vendors who have the same sort of concerns about demonstrable usability.

If some changes in this are not quite up to standard, please ensure to give some sort of opportunity to rectify them before closing this PR.

[kentfredric]

Tests are now passing on all but 1.0.0, which is broken because it can't sync cargo.