filters shouldn't be dependent on available dimensions

[bbyrd]

Right now, the gem only lets you filter on a dimension that's being used in the query. But based on the Query Explorer (http://code.google.com/apis/analytics/docs/gdata/gdataExplorer.html), it doesn't appear that the filters need to be dependent on the selected dimensions...

.rvm/gems/ruby-1.8.7-p352/gems/gattica-0.4.3/lib/gattica.rb:359:in `validate_and_clean': You are trying to filter by fields that are not in the available dimensions or metrics: source == google (GatticaError::InvalidSort)

It seems logical to de-link these in the gem, because it would free up extra dimensions for reporting; otherwise, the filtered dimension is pretty much a waste of space. For example, if I'm looking for only Google / CPC data, there's no reason why I should have filtered columns that all read "google", "cpc"...

Thanks for the work, btw! It's saved me a lot of time with a project I'm working on...