pinpad entry support in Git repository

[NIIBE Yutaka]

Hi, 

In the Git repository of GnuPG (of master branch), I added pinpad
input support for PC/SC.  It is enabled for OpenPGPcard 2.0.

Could you please test it out?

	(1) pinpad input for verify for user
	(2) pinpad input for verify for admin
	(3) pinpad input for passphrase modification by user
	(4) pinpad input for passphrase modification by admin

Please let me know your reader and its features (has display or not).

If it is stable enough, I would like to apply changes to stable
branch.

Thanks in advance.
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