These functions can now take an object or a type (class).

If given an object, they will wrap subsequent calls to that object.
If given a type, they will return an object that can be instantiated
to create a new object, and all calls including __init__ will be
covered by the serialization or thread verification.

Like the serializer changes, the class decorator was too fragile.

Occasional segfaults may be the result of performing thread-unsafe
operations.  This class decorator verifies that all of its methods
are called in a thread-safe manner.

It can separately warn about:
- two threads calling methods in a function (the kind of thing sqlite
  doesn't like)
- recursion
- concurrency (two different threads functions at the same time)