Make Composite roles always return false for is_anon

This fixes warnings that you can get with Perl 5.16 and earlier when combining
parameterized roles with other roles:

    package Class;
    use Moose;
    with 'ParameterizedRole', 'SomeOtherRole';
Add Moose::Meta::Role::Composite->is_anon to list of methods that we don't need coverage for
Merge pull request #69 from moose/topic/composite-is-not-anon

Make Composite roles always return false for is_anon