Bug Fix - #231 time_t/int collision on 32-bit systems

- Fixed bug #231 by removing the operator int () cast from the Duration
  class.  On a 32-bit system, "time_t" may be defined as "int", in
  which case the int cast and time_t cast are essentially duplicates.
  Thanks to Pietro Cerutti, who also provided a patch.

AUTHORS

@@ -17,6 +17,7 @@ The following submitted code, packages or analysis, and deserve special thanks:
   P.C. Shyamshankar
   Johan Friis
   Steven de Brouwer
+  Pietro Cerutti
 
 Thanks to the following, who submitted detailed bug reports and excellent suggestions:
   Eugene Kramer