New log driver; buffers messages and makes them available to userland.

Added some fields in the generic device table to support this driver
using libdriver. Updated other drivers to fill these fields with nops
and NULLs.

drivers/floppy/floppy.c

@@ -274,6 +274,10 @@ PRIVATE struct driver f_dtab = {
   f_geometry,	/* tell the geometry of the diskette */
   floppy_stop,	/* floppy cleanup on shutdown */
   f_expire_tmrs,/* expire all alarm timers */
+  nop_fkey,	/* ignore function keys and CANCELs */
+  nop_cancel,
+  nop_select,
+  NULL
 };