Two essential changes were made to the process of initially downloading
the blacklist at install time, allowing the removal of a number of hacks
and workarounds:
1. Download the files *after* populating the build directory instead of
*before*. Thus, the files don't have to be included in MANIFEST.in, and
following from that, `setup.py sdist` needn't be tricked into not
including them in the source distribution.
2. Only import the updater module instead of the full validate_email
package, so `setup.py install` and friends don't depend on all the
requirements of the library.
