mocked - use mocked libraries in unit tests

Synopsis:

  # use a fake LWP::Simple for testing from t/lib/LWP/Simple.pm
  use mocked 'LWP::Simple';
  my $text = get($url);


Often during unit testing, you may find the need to use mocked libraries
to test edge cases, or prevent unit tests from using slow or external
code.

This is where mocking libraries can help.

When you mock a library, you are creating a fake one that will be used
in place of the real one.  The code can do as much or as little as is
needed.

Use mocked.pm as a safety measure (so it actually loads the right
module), and as a way to document the tests for future maintainers.
