imports e.g. test_support must do so using an absolute package name
such as "import test.test_support" or "from test import test_support".

This also updates the README in Lib/test, and gets rid of the
duplicate data dirctory in Lib/test/data (replaced by
Lib/email/test/data).

Now Tim and Jack can have at it. :)

- Use substring search, not re search for user-agent and paths.
- Consider * entry last. Unquote, then requote URLs.
- Treat empty Disallow as "allow everything".
Add test cases. Fixes #523041