( resource id )
Returns an error number for the server (last request) identified by
yaz_errno() should be called after network activity for
each server - (after yaz_wait() returns) to determine the
success or failure of the last operation (e.g. search).
Returns an error code. The error code is either a Z39.50 diagnostic code
(usually a Bib-1 diagnostic) or a client side error code which is
generated by PHP/YAZ itself, such as "Connect failed", "Init Rejected",