title: thinking sphinx: syntax error in date range
body: <p>I have the following index:</p>
  
  <pre><code>ThinkingSphinx::Index.define :offer, :with =&gt; :active_record do
  
    indexes tags(:name), as: :tags
    indexes :name, as: :offer_name
    indexes :description, as: :offer_description
  
    has enabled, as: :offer_enabled
  
    has customer.is_enabled, as: :customer_enabled
    has customer.is_accepted, as: :customer_accepted
  
    has category.id, as: :category_id
    has :to, as: offer_to
  
  end
  </code></pre>
  
  <p>Now when making a search and using a Date range for an attribute like</p>
  
  <pre><code>Offer.search( 'some search terms', with: { to: Date.current..(Date.current + 12.months), category_id: 3 } )
  </code></pre>
  
  <p>I get the following error message:</p>
  
  <pre><code>sphinxql: syntax error, unexpected '-', expecting AND near '-12-27 AND 2014-12-27 AND `category_id` = 9 AND `sphinx_deleted` = 0 LIMIT 0, 50; SHOW META'
  </code></pre>
  
  <p>I am using: </p>
  
  <p>sphinx version 2.1.3 
  thinking sphinx version 3.0.6
  rails 4.0.2</p>