Updating CHANGES for 1.0.21 release

CHANGES

 = Changes from previous Cobalt Versions =
 
+== Changes to 1.0.21 ==
+ * Fixed numerous locking issues in job startup that could result in a small chance
+   of failed job initialization.
+ * Fixed an issue on Cray systems where brief network disruptions on service nodes
+   can cause a loss of contact with a forker resulting in a loss of the running jobs.
+ * Added additional logging for ProxyErrors.  The original trace/error message should
+   now be presented to the caller in the event of a ProtocolError.
+ * Fixed an issue in the cdbwriter where an error in writing job attributes could
+   cause a recurring error loop preventing database updates.
+
 == Changes to 1.0.20 ==
  * Fix for certain IO error messages that were ambiguous.
  * Fix for an issue where attrs on a job are changed as a part of a filter script while