Add wxWindow::EnableTouchEvents()

Don't request touch event generation for all windows by default, this
has an inherent overhead and is not needed for 99% of the application
windows, so require calling EnableTouchEvents() explicitly to do it
instead.

Note that this requires properly initializing gesture recognizers in
wxOSX now that they're not always allocated, otherwise releasing them
when destroying the window would crash.

include/wx/window.h

@@ -133,6 +133,13 @@ enum wxShowEffect
     wxSHOW_EFFECT_MAX
 };
 
+// Values for EnableTouchEvents() mask.
+enum
+{
+    wxTOUCH_NONE            = 0x0000,
+    wxTOUCH_ALL_GESTURES    = 0x00ff
+};
+
 // flags for SendSizeEvent()
 enum
 {
@@ -1033,6 +1040,13 @@ public:
     virtual bool HasCapture() const
         { return (wxWindow *)this == GetCapture(); }
 
+        // enable the specified touch events for this window, return false if
+        // the requested events are not supported
+    virtual bool EnableTouchEvents(int WXUNUSED(eventsMask))
+    {
+        return false;
+    }
+
     // painting the window
     // -------------------