Attempted fix for overzealous refactoring.

a37c4e1 factored out

    read_attribute(:datetime_value)

to #datetime_value.  Unfortunately, this shadows ActiveRecord's
definition of #datetime_value (which is auto-generated).  Hypothesis:
this is causing things like timezone conversion to be eliminated from
the attribute reader.

lib/surveyor/models/response_methods.rb

@@ -51,7 +51,7 @@ def correct?
       end
 
       def time_value
-        datetime_value.try(:strftime, time_format)
+        read_attribute(:datetime_value).strftime( time_format ) unless read_attribute(:datetime_value).blank?
       end
 
       def time_value=(val)
@@ -64,7 +64,7 @@ def time_value=(val)
       end
 
       def date_value
-        datetime_value.try(:strftime, date_format)
+        read_attribute(:datetime_value).strftime( date_format ) unless read_attribute(:datetime_value).blank?
       end
 
       def date_value=(val)
@@ -76,10 +76,6 @@ def date_value=(val)
           end
       end
 
-      def datetime_value
-        read_attribute(:datetime_value)
-      end
-
       def time_format
         '%H:%M'
       end
@@ -102,7 +98,7 @@ def to_formatted_s
                when :time
                  time_value
                when :datetime
-                 datetime_value.try(:strftime, datetime_format) || ''
+                 (read_attribute(:datetime_value).strftime( datetime_format ) unless read_attribute(:datetime_value).blank?) || ''
                else
                  to_s
                end