really revert endpoint_t -> int

debugging info on panic: decode segment selectors and descriptors, now moved
to arch-specific part, prototypes added; sanity checking in debug.h made
optional with vmassert().

kernel/utility.c

@@ -48,12 +48,6 @@ if (minix_panicing++) {
 	kprintf("\n");
   }
 
-  printseg("cs: ", 1, NULL, read_cs());
-  printseg("ds: ", 0, NULL, read_ds());
-  if(read_ds() != read_ss()) {
-	  printseg("ss: ", 0, NULL, read_ss());
-  }
-
   kprintf("kernel: ");
   util_stacktrace();