WinVideo: share some generic code (PR #901)

* WinVideo: move some generic functions back to Video.

Introduce a new virtual function (VideoPresentScreen) to draw the video buffer to video memory.

* Move Win32Frame::VideoRedrawScreen() to FrameBase as it is generic.

source/FrameBase.cpp

@@ -1,6 +1,7 @@
 #include "StdAfx.h"
 
 #include "FrameBase.h"
+#include "Interface.h"
 
 FrameBase::FrameBase()
 {
@@ -15,3 +16,9 @@ FrameBase::~FrameBase()
 {
 
 }
+
+void FrameBase::VideoRedrawScreen(void)
+{
+	// NB. Can't rely on g_uVideoMode being non-zero (ie. so it can double up as a flag) since 'GR,PAGE1,non-mixed' mode == 0x00.
+	GetVideo().VideoRefreshScreen(GetVideo().GetVideoMode(), true);
+}