title: :greater_than_or_equal_to in validates_numericality_of only partially working in rails 3.1
body: <p>We are using the following to check if stock_qty (an integer or a float. Could be zero but not nil) is greater or equal to zero:</p>
  
  <pre><code>validates_numericality_of :stock_qty, :greater_than_or_equal_to =&gt; 0
  validates_numericality_of :stock_qty, :less_than_or_equal_to =&gt; :in_qty, :if =&gt; Proc.new { |part| !part.in_qty.nil? }
  </code></pre>
  
  <p>:in_qty is a column in part model. This validation should allow positive or 0 for :stock_qty. The problem is that the rspec failed if :stock_qty is assigned zero. I noticed that :less_than_or_equal_to only allowed less_than and did not allow equal_to. Is there a way to validate the >= or &lt;= in rails 3.1? Or what may go wrong with our validation code above. Thanks so much. </p>