Disallow non-text name passed to adapter registry methods.

Prevents corruption of lookup cache.

Alternative to fix proposed in #75 (3.6 branch).

Added Travis, appveyor, and tox for 3.6 branch.

Copied from master branch, but removed the Python 3 stuff,
which is unsupported on the 3.6 branch. Well, 3.1 seems supported,
but that is very old, and on 3.3 I got errors locally.

Also removed 'docs' from the tox envs, as that proved tricky to get to work,
and has changed much.

Removed 'TODO_test_classProvides_fails_for_odd_class' test method,
which would always fail but be ignored due to its name,
except that the coverage tests would *not* ignore it, leading to a failure.