Use the PRI_NEW_SET_API define provided by >=libpri-1.2 to distinguish
between old style and new style pri_set_error() and pri_set_message()
callback functions.

Improve message logging by using ftdm_log_chan() if per-span
data with a valid (d-)channel object is available.
NOTE: pri_get_userdata() returns NULL if pri is NULL.

This will reduce the horizontal space for libpri output a bit, but allows
us to see which span the message/error came from.
Signed-off-by: Stefan Knoblich <stkn@openisdn.net>