Implement list_files for CardOS5 cards.

Hello, I wrote a commit which depends on the changes you already wrote for CardOS5. Would you add it on the top of the pull-request you have in the upstream repository of OpenSC?

The only difference with list_files for the CardOS4 cards is that the length-field takes 2 bytes (even though the documentation states it should be 1 byte). The commit can be tested with "opensc-explorer" by typing "ls".