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/codegen_x86.c

@@ -563,6 +563,11 @@ void codegen_init()
         mem_store_addr_ea_b = gen_MEM_STORE_ADDR_EA_B();
         block_pos = 1024;
         mem_store_addr_ea_q = gen_MEM_STORE_ADDR_EA_Q();
+        
+        asm(
+                "fstcw %0\n"
+                : "=m" (cpu_state.old_npxc)
+        );
 }
 
 void codegen_reset()