PIV - Improved error handling of get_challenge
PIV - Improved error handling of get_challenge

Random data from PIV card is obtained using GENERAL AUTHENTICATE command
for a request of a Challenge from the card. "00 87 00 9B 04 7C 02 81 00"
Usually 8 bytes are returned.

NIST 800-73-3_PART2, "A.1 Authentication of the PIV Card Application Administrator"
"Table 11. Authentication of PIV Card Application Administrator" shows an example of
how to do this.

Some cards (one I have: 3b:7d:96:00:00:80:31:80:65:b0:83:11:17:d6:83:00:90:00)
will not allow 2 of these commands in a row. (Maybe assuming command is only
used as in Table 11 and is expecting the second command.)

Code was added to card-piv.c so if "6A 80" is returned, try the command one more time.
For any other GENERAL AUTHENTICATE failure, SC_ERROR_NOT_SUPPORTED is returned.
piv_get_challenge may be called within a loop from sc_get_challenge if more random
data is needed thus causing the the 2 commands to sent in a row.

On branch piv-improved-matching
 Changes to be committed:
	modified:   card-piv.c

mouse07410/OpenSC,mouse07410/OpenSC,mouse07410/OpenSC