2.9.81

* DataModel: describe_column(): Use refreturn to avoid 
  a reference-counting problem.
* Connection: Added execute_select_command() and execute_non_select_command() that 
  take the command as a string and that take a parameter list, for convenience.
* ParameterList: Remove add_param_*() methods, because we already have add_parameter() 
  methods that wrap the same C functions. Ref the return, to avoid a crash.
  None of these could have worked before.
* ConnectionEvent: Put the enums inside the Gnome::Gda namespace 
  instead of inside Gnome::.
* Value:
  Added get_ulong() and set_ulong() and a constructor.
  (Murray Cumming)
* Build: Fix build when exceptions are disabled in glibmm.
  (Armin Burgmeier)
* Documentation: Added simple_iter example to show the use 
  of ITER_MODEL_ONLY models.
  (Murray Cumming)