Fix custom external fact loader's weights
Fix custom external fact loader's weights

Because facter doesn't expose the weight as a customizable value, we
need to override the constant. You can't do that in a subclass:

```ruby
class A
  FOO="A"
  def foo; FOO; end
end

class B < A
  FOO="B"
end

A.new.foo # => "A"
B.new.foo # => "A"

class A
  def foo; self.class::FOO; end
end

A.new.foo # => "A"
B.new.foo # => "B"
```

So, we copy the `#load` method :(

namesco/puppet-boxen,theand-boxen/puppet-boxen,namesco/puppet-boxen,salimane/puppet-boxen,indirect/puppet-boxen,indirect/puppet-boxen,halyard/puppet-boxen,siddhuwarrier/puppet-boxen,salimane/puppet-boxen,siddhuwarrier/puppet-boxen,halyard/puppet-boxen,dieterdemeyer/puppet-boxen,boxen/puppet-boxen,theand-boxen/puppet-boxen,theand-boxen/puppet-boxen,dieterdemeyer/puppet-boxen,namesco/puppet-boxen,indirect/puppet-boxen,boxen/puppet-boxen,boxen/puppet-boxen,n0ts/puppet-boxen,n0ts/puppet-boxen,siddhuwarrier/puppet-boxen,halyard/puppet-boxen,n0ts/puppet-boxen,dieterdemeyer/puppet-boxen