* disk/i386/pc/biosdisk.c (pupa_biosdisk_open): Correctly check
for available extensions.
* include/pupa/i386/pc/time.h: New file.
* kern/disk.c: Include <pupa/machine/time.h>.
(PUPA_CACHE_TIMEOUT): New macro.
(pupa_last_time): New variable.
(pupa_disk_open): Flush the cache when there was a timeout.
(pupa_disk_close): Reset the timer.
* kern/i386/pc/startup.S (pupa_get_rtc): Renamed from
pupa_currticks.
* util/misc.c: Include <sys/times.h>
(pupa_get_rtc): New function.