pcmcia - spot slave decode flaws (for testing)

It tries to spot when the slave is a mirror of the master and to fix up
problems that causes.

I've got two confirmations so far that this plus the "can fail set_xfer" patch
work for folks who had problems before.  Also if you are unfortunate enough to
be running something like HAL then it'll automount the same disk twice for you
and corrupt it without the fix (aint that nice...)

Tested (successfully) by Komuro <komurojun-mbn@nifty.com>.

Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>