scd-backport-2-0 branch

[NIIBE Yutaka]

On 2012-06-22 at 11:49 +0900, NIIBE Yutaka wrote:
> I backported SCD (scdaemon) related changes to scd-backport-2-0
> branch.  If it doesn't have any problem, I'd like to merge it into
> STABLE-BRANCH-2-0.

BTW, during the work of backport, I couldn't understand the reason why
scdaemon remains after removal of card (or removal of card reader /
token).  I think that it is easier to just shutdown scdaemon when
it detects removal of card.

Please teach me about the design of scdaemon.
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