Non-PRI_NEW_SET_API logging callbacks were only available in libpri-1.0 and older,
which also lacks PRI_IO_FUNCS (required) and wouldn't work anyway.

Explicitly check for both PRI_* feature defines at configure time and reject libpri
versions that lack them.

Remove the non-PRI_NEW_SET_API logging callbacks in ftmod_libpri.c.
Signed-off-by: Stefan Knoblich <stkn@openisdn.net>