* g10/ecdh.c (pk_ecdh_encrypt_with_shared_point): Factor extraction
part out to  ...
(extract_secret_x): new.  Allow for x-only coordinate.
(pk_ecdh_encrypt_with_shared_point): Change arg shared_mpi
to (shared,nshared).  Move param check to the top.  Add extra safety
check.
(pk_ecdh_decrypt): Adjust for change.
* g10/pkglue.c (get_data_from_sexp): New.
(pk_encrypt): Use it for "s" and adjusted for changed
pk_ecdh_encrypt_with_shared_point.
* g10/pubkey-enc.c (get_it): Remove conversion to an MPI and call
pk_ecdh_decrypt with the frame buffer.