patch 8.0.1449: slow redrawing with DirectX

Problem:    Slow redrawing with DirectX.
Solution:   Avoid calling gui_mch_flush() unnecessarily, especially when
            updating the cursor. (Ken Takata, closes #2560)
diff --git a/src/term.c b/src/term.c
index ffa3944..6303e10 100644
--- a/src/term.c
+++ b/src/term.c
@@ -2501,6 +2501,27 @@
     }
 }
 
+/*
+ * out_flush_cursor(): flush the output buffer and redraw the cursor
+ */
+    void
+out_flush_cursor(
+    int	    force UNUSED,   /* when TRUE, update cursor even when not moved */
+    int	    clear_selection UNUSED) /* clear selection under cursor */
+{
+    mch_disable_flush();
+    out_flush();
+    mch_enable_flush();
+#ifdef FEAT_GUI
+    if (gui.in_use)
+    {
+	gui_update_cursor(force, clear_selection);
+	gui_may_flush();
+    }
+#endif
+}
+
+
 #if defined(FEAT_MBYTE) || defined(PROTO)
 /*
  * Sometimes a byte out of a multi-byte character is written with out_char().