Rewritten parts of the 86F handler to minimize false CRC errors and misidentification of sectors;

Replaced IMG handler with one that now proxies to the 86F handler;
Applies the remaining Mainline PCem speedup commit;
Fixed the National Semiconductors PC87306 Super I/O Chip's serial port IRQ assignment;
DMF images are now loaded with the correct sector interleave, improving read/write speed;
XDF images are now loaded in a way that emulates the real order of the sectors on the track, improving read/write speed;
Added 16-bit physical memory read/write routines (mem_phys_readw, mem_phys_writew) and modified the 16-bit DMA code to use them instead of two 8-bit reads/writes.

src/ibm.h

@@ -167,6 +167,8 @@ struct
         uint16_t MM_w4[8];
         
         MMX_REG MM[8];
+        
+        uint16_t old_npxc, new_npxc;
 } cpu_state;
 
 #define cycles cpu_state._cycles
@@ -575,6 +577,8 @@ extern uint32_t atapi_get_cd_volume(int channel);
 
 extern int ide_ter_enabled;
 
+extern int ui_writeprot[2];
+
 void pclog(const char *format, ...);
 extern int nmi;