Add shortcuts for the combobox (select all, copy, cut, paste)

* It is the same as the code in the implementation of the wxTextCtrl, I
  guess this could be extracted in a common function, but I don't know
  where to put it.

include/wx/osx/combobox.h

@@ -130,11 +130,17 @@ protected:
 
     virtual void EnableTextChangedEvents(bool enable) wxOVERRIDE;
 
+    // callbacks
+    void OnKeyDown(wxKeyEvent& event); // Process clipboard shortcuts
+
     // the subcontrols
     wxComboBoxText*     m_text;
     wxComboBoxChoice*   m_choice;
 
     wxComboBoxDataArray m_datas;
+
+private:
+    wxDECLARE_EVENT_TABLE();
 };
 
 #endif // _WX_COMBOBOX_H_

src/osx/combobox_osx.cpp

@@ -18,6 +18,12 @@
 #ifndef WX_PRECOMP
 #endif
 
+typedef wxWindowWithItems<wxControl, wxComboBoxBase> RealwxComboBoxBase;
+
+wxBEGIN_EVENT_TABLE(wxComboBox, RealwxComboBoxBase)
+    EVT_KEY_DOWN(wxComboBox::OnKeyDown)
+wxEND_EVENT_TABLE()
+
 // work in progress
 
 wxComboBox::~wxComboBox()
@@ -234,4 +240,33 @@ void wxComboBox::Dismiss()
     GetComboPeer()->Dismiss();
 }
 
+void wxComboBox::OnKeyDown(wxKeyEvent& event)
+{
+    if (event.GetModifiers() == wxMOD_CONTROL)
+    {
+        switch(event.GetKeyCode())
+        {
+            case 'A':
+                SelectAll();
+                return;
+            case 'C':
+                if (CanCopy())
+                    Copy();
+                return;
+            case 'V':
+                if (CanPaste())
+                    Paste();
+                return;
+            case 'X':
+                if (CanCut())
+                    Cut();
+                return;
+            default:
+                break;
+        }
+    }
+    // no, we didn't process it
+    event.Skip();
+}
+
 #endif // wxUSE_COMBOBOX && wxOSX_USE_COCOA