Merge branch 'msw-double-buffer'

Improve double-buffering support in wxMSW wxListCtrl and optionally use
it in wxTreeCtrl too.

Closes https://github.com/wxWidgets/wxWidgets/pull/636

include/wx/msw/missing.h

@@ -244,6 +244,10 @@
     #define TV_FIRST                0x1100
 #endif
 
+#ifndef TVS_EX_DOUBLEBUFFER
+    #define TVS_EX_DOUBLEBUFFER     0x0004
+#endif
+
 #ifndef TVS_FULLROWSELECT
     #define TVS_FULLROWSELECT       0x1000
 #endif
@@ -253,6 +257,11 @@
     #define TVM_SETTEXTCOLOR        (TV_FIRST + 30)
 #endif
 
+#ifndef TVM_SETEXTENDEDSTYLE
+    #define TVM_SETEXTENDEDSTYLE    (TV_FIRST + 44)
+    #define TVM_GETEXTENDEDSTYLE    (TV_FIRST + 45)
+#endif
+
 // Various defines used by the webview library that are needed by mingw 
 
 #ifndef DISPID_COMMANDSTATECHANGE