set Gregorian calendar

fixes: #635 (comment)

models/aether_lat-lon/model_mod.f90

@@ -15,7 +15,7 @@ module model_mod
     r8, i8, MISSING_R8, vtablenamelength
 
 use time_manager_mod, only : &
-    time_type, set_time
+    time_type, set_time, set_calendar_type
 
 use location_mod, only : &
     location_type, get_close_type, &
@@ -165,6 +165,8 @@ subroutine static_init_model()
 read(iunit, nml = model_nml, iostat = io)
 call check_namelist_read(iunit, io, "model_nml")
 
+call set_calendar_type('GREGORIAN')
+
 ! Record the namelist values used for the run 
 if (do_nml_file()) write(nmlfileunit, nml=model_nml)
 if (do_nml_term()) write(     *     , nml=model_nml)