Feature: allow a toggle to enable/disable vsync

Vsync should be off by default, as for most players it will be
better to play without vsync. Exception exist, mainly people who
play in fullscreen mode.

src/table/misc_settings.ini

@@ -77,6 +77,12 @@ var      = _video_hw_accel
 def      = true
 cat      = SC_BASIC
 
+[SDTG_BOOL]
+name     = ""video_vsync""
+var      = _video_vsync
+def      = false
+cat      = SC_BASIC
+
 [SDTG_OMANY]
 name     = ""support8bpp""
 type     = SLE_UINT8