Bug1338 fixed again, with fewer Mac busy-waits; CHANGES WX BUILD...

... Busy-waiting will happen on Mac when modal dialogs are open, and a LADSPA,
VST, or AudioUnits effect is also open with "fancy" interface.

Busy-waiting will not happen for modal dialogs at other times.

src/effects/lv2/LV2Effect.cpp

@@ -18,6 +18,11 @@
 #include <wx/dcbuffer.h>
 #include <wx/dialog.h>
 #include <wx/dynarray.h>
+
+#ifdef __WXMAC__
+#include <wx/evtloop.h>
+#endif
+
 #include <wx/math.h>
 #include <wx/msgdlg.h>
 #include <wx/sizer.h>
@@ -1133,6 +1138,10 @@ bool LV2Effect::HideUI()
 
 bool LV2Effect::CloseUI()
 {
+#ifdef __WXMAC__
+   wxEventLoop::SetBusyWaiting(false);
+#endif
+
    mParent->RemoveEventHandler(this);
 
    if (mSliders)
@@ -1561,6 +1570,10 @@ bool LV2Effect::BuildFancy()
 
    TransferDataToWindow();
 
+#ifdef __WXMAC__
+   wxEventLoop::SetBusyWaiting(true);
+#endif
+
    return true;
 }