Move the changes test to xt

This really shouldn't be run by end users. It failed for someone I work with,
probably because of the version of Test::CPAN::Changes he had installed.
Merge pull request #21 from maxmind/dave/no-changes-test-for-end-user

Merging for 0.007000.

Move the changes test to xt
Merge pull request #25 from manchicken/master

Version 0.007000 is ready