Updated valid to/from dates. refs #3648 & #1906

Code/Mantid/instrument/CNCS_Definition.xml

 <?xml version='1.0' encoding='ASCII'?>
-<instrument valid-to="2100-01-31 23:59:59" name="CNCS" valid-from="2011-08-31 14:17:47.233794">
+<instrument valid-to="2100-01-31 23:59:59" name="CNCS" valid-from="2011-08-17 13:17:41">
   <!--for runs after 35154-->
   <defaults>
     <length unit="metre"/>

Code/Mantid/instrument/CNCS_Definition_upto_35154.xml

@@ -2,7 +2,7 @@
 <!-- For help on the notation used to specify an Instrument Definition File 
      see http://www.mantidproject.org/IDF -->
 <instrument name="CNCS" valid-from   ="1900-01-31 23:59:59"
-                        valid-to     ="2100-01-31 23:59:59"
+                        valid-to     ="2011-08-17 13:17:00"
 		        last-modified="2010-10-12 08:54:11">
   <!--Created by Michael Reuter-->
   <defaults>