Fixed include of os.h

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@692 dfc29bdd-3216-0410-991c-e03cc46cb475

source/Irrlicht/COpenGLExtensionHandler.cpp

 #include "COpenGLExtensionHandler.h"
-#include "os.h"
 #include "irrString.h"
 #include "SMaterial.h" // for MATERIAL_MAX_TEXTURES
 

source/Irrlicht/COpenGLExtensionHandler.h

@@ -7,6 +7,7 @@
 
 #include "EDriverFeatures.h"
 #include "irrTypes.h"
+#include "os.h"
 
 #if defined(_IRR_WINDOWS_API_)
 	// include windows headers for HWND