* src/cms.h (struct enc_val_s): Add new fields for ECDH.
* src/cms.c: Include der-builder.h
(log_sexp): New but commented debug helper.
(ksba_cms_release): Free new ECDH values.
(ksba_cms_set_enc_val): Support ECDH.
(build_enveloped_data_header): Rewrite to make use of the new DER
builder.