* resolv/res_mkquery.c: Define __res_nopt.
* resolv/res_query.c (__libc_res_nquery): If RES_USE_EDNS0 is set
try adding EDNS0 record.
* resolv/res_send.c (send_dg): If request failed with FORMERR and
EDNS0 record was send make sure we don't try it again.
* resolv/resolv.h: Define RES_F_EDNS0ERR and RES_USE_EDNS0.
* include/resolv.h: Declare __res_nopt.