Fix printing of ECC algo names in hkp keyserver listings.

* g10/misc.c (map_pk_openpgp_to_gcry): New.
* g10/keyserver.c (print_keyrec): Map OpenPGP algorithm ids.

Although we don't have support for ECC, we want to print a proper
algorithm name in keyserver listings. This will only work while using
a ECC enabled Libgcrypt. Problem reported by Kristian Fiskerstrand.