g10: fix cmp_public_key and cmp_secret_keys.
* g10/free-packet.c (cmp_public_keys, cmp_secret_keys): Compare opaque data at the first entry of the array when it's unknown algo. * mpi/mpi-cmp.c (mpi_cmp): Backport libgcrypt 1.5.0's semantics.
(backported from 2.0 commit 43429c7869152f301157e4b24790b3801dce0f0a)
- GnuPG-bug-id: T1962