[#4420] Display per period Retainer values on the Contract details page.

app/models/fixed_deliverable.rb

@@ -29,8 +29,8 @@ class FixedDeliverable < Deliverable
 
   # The amount of money remaining after expenses have been taken out
   # Profit left = Total - Labor spent - Overhead spent
-  def profit_left
-    total_spent - labor_budget_spent - overhead_spent
+  def profit_left(date=nil)
+    total_spent(date) - labor_budget_spent(date) - overhead_spent(date)
   end
   
   # Hardcoded value used as a wrapper for the old Budget plugin API.