Added wxUSE_DC_CACHEING and associated code to wxMSW

Added EnableCache, CacheEnabled to wxDCBase
Added mask source args to DoBlit, Blit
Added cache testing code to dragimag sample
Added wxSystemOptions, regenerated makefiles


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@10962 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

samples/dragimag/dragimag.h

@@ -46,6 +46,7 @@ class MyApp: public wxApp
 public:
     MyApp();
     virtual bool OnInit();
+    virtual int OnExit();
 
 //// Operations