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/mem.c

@@ -1552,6 +1552,16 @@ uint8_t mem_readb_phys(uint32_t addr)
         return 0xff;
 }
 
+uint16_t mem_readw_phys(uint32_t addr)
+{
+        mem_logical_addr = 0xffffffff;
+        
+        if (_mem_read_w[addr >> 14]) 
+                return _mem_read_w[addr >> 14](addr, _mem_priv_r[addr >> 14]);
+                
+        return 0xff;
+}
+
 void mem_writeb_phys(uint32_t addr, uint8_t val)
 {
         mem_logical_addr = 0xffffffff;
@@ -1560,6 +1570,14 @@ void mem_writeb_phys(uint32_t addr, uint8_t val)
                 _mem_write_b[addr >> 14](addr, val, _mem_priv_w[addr >> 14]);
 }
 
+void mem_writew_phys(uint32_t addr, uint16_t val)
+{
+        mem_logical_addr = 0xffffffff;
+        
+        if (_mem_write_w[addr >> 14]) 
+                _mem_write_w[addr >> 14](addr, val, _mem_priv_w[addr >> 14]);
+}
+
 uint8_t mem_read_ram(uint32_t addr, void *priv)
 {
 //        if (addr >= 0xc0000 && addr < 0x0c8000) pclog("Read RAMb %08X\n", addr);