fixes a lot of warnings which pass a const buffer to the APDU's data

Note that a non-const data member is only required for sc_allocate_apdu
sc_free_apdu. They are currently used with an explicit typecast.
However, sc_allocate_apdu and sc_free_apdu both are not used once in the
entire project. One might also simply throw both functions away.

The structures PIN_MODIFY_STRUCTURE and PIN_VERIFY_STRUCTURE now use a
C99 flexible array member when available for abData field.

uint8_t abData[];

See http://lists.alioth.debian.org/pipermail/pcsclite-cvs-commit/2013-May/006191.html