Added a helper method to TimeEntry that will encapsulate the rate API for a TimeEntry.

* TimeEntry#cost will return the amount the TimeEntry costs based on:
** logged hours times the assigned rate amount
** logged hours times the effective project rate for the user
** logged hours times the effective default rate for the user
** 0 if the user has no rates at all

  #1924

lib/rate_time_entry_patch.rb

@@ -0,0 +1,38 @@
+require_dependency 'time_entry'
+
+module RateTimeEntryPatch
+  def self.included(base) # :nodoc:
+    base.extend(ClassMethods)
+
+    base.send(:include, InstanceMethods)
+
+    # Same as typing in the class 
+    base.class_eval do
+      unloadable # Send unloadable so it will not be unloaded in development
+      belongs_to :rate
+      
+    end
+
+  end
+  
+  module ClassMethods
+    
+  end
+  
+  module InstanceMethods
+    # Returns the current cost of the TimeEntry based on it's rate and hours
+    def cost
+      if self.rate.nil?
+        amount = Rate.amount_for(self.user, self.project, self.spent_on.to_s)
+      else
+        amount = rate.amount
+      end
+
+      return 0.0 if amount.nil?
+      
+      return amount.to_f * hours.to_f
+    end
+  end
+end
+
+TimeEntry.send(:include, RateTimeEntryPatch)