get_pin for scard-opensc.c

[Nils Larsch]

Markus Friedl wrote:
> i think that if you want to use pin protected cards the ssh-agent
> should be used. ssh-add will prompt for the pin.

There's one small problem with this approach: if you
have more than one key protected with different pins
this doesn't really work, because ssh-agent.c asks for
the pin before the keys are loaded with sc_get_keys()
(scard-opensc.c).

Nils