Do not assume nfc_initiator_select_tag() and nfc_initiator_deselect_tag() will not return an error if the provided tag is supposed to be ready for the operation (it might have move out of the field), and let the error propagate through libfreefare to the application calling the functions.
Endianness fun is not provided by the same header file on GNU/Linux (endian.h) and FreeBSD (sys/endian.h). Add some magic for the autotools to detect the correct header file. While here, add AC_C_INLINE: it's reported as missing by autoscan(1).