Mystique fixes :

- MGA mode disables all VGA data processing on reads / writes
- MGA mode forces 8 pixels per character
- DMAPAD acts as an ILOAD mirror during ILOAD operations, same as SRCx
- Handle signed X coordinates better in blit operations
- Add more MMIO registers
- Don't fatal on ILOAD reads when blitter not busy
Fixes Windows XP with Mystique.

src/vid_svga.h

@@ -77,6 +77,7 @@ typedef struct svga_t
         int linepos, vslines, linecountff, oddeven;
         int con, cursoron, blink;
         int scrollcache;
+        int char_width;
         
         int firstline, lastline;
         int firstline_draw, lastline_draw;