Changed CONTEXT into CONTEXT86 everywhere we really want an i386
context.
Added #ifdef __i386__ around accesses to 386 registers in the generic
CONTEXT structure.

diff --git a/msdos/int13.c b/msdos/int13.c
index c577fa4..7fff05e 100644
--- a/msdos/int13.c
+++ b/msdos/int13.c
@@ -23,7 +23,7 @@
  *
  * Handler for int 13h (disk I/O).
  */
-void WINAPI INT_Int13Handler( CONTEXT *context )
+void WINAPI INT_Int13Handler( CONTEXT86 *context )
 {
     switch(AH_reg(context))
     {