Add a simple test for the packaging RECORD file.

Add a simple test for the packaging RECORD file.

The existing test_record is not easily extendable to add script files or
extension modules: it collects all files from fake_dists and generates a
RECORD file at runtime.  I felt more comfortable adding a new test
written from scratch more self-contained (just one project with
well-defined files) and more stupid (the checksums and sizes are
computed once and hard-coded).