Fix the integer value in events generated by generic wxSpinCtrl

This notably fixes the problem with changing the year using spin control
arrows under macOS, where this control is used as part of
wxGenericCalendarCtrl, as not having the correct value in the event object
resulted in bogus events with dates in the year 0 there.

See http://trac.wxwidgets.org/ticket/17193

(cherry picked from commit 148e8971c7)

docs/changes.txt

@@ -679,6 +679,7 @@ wxOSX:
 - Return false from wxSound::Create()/IsOk() if the file doesn't exist.
 - Fix scrolling behaviour of wxSearchCtrl (John Roberts).
 - Add wxTE_{RIGHT,CENTER} support for multiline wxTextCtrl (Andreas Falkenhahn).
+- Fix changing year in wxCalendarCtrl using arrows (Lauri Nurmi).
 
 
 3.0.2: (released 2014-10-06)

src/generic/spinctlg.cpp

@@ -96,6 +96,7 @@ public:
         wxCommandEvent eventCopy(event);
         eventCopy.SetEventObject(m_spin);
         eventCopy.SetId(m_spin->GetId());
+        eventCopy.SetInt(wxAtoi(event.GetString()));
         m_spin->ProcessWindowEvent(eventCopy);
     }