(lookup_hostkey_algorithm): New function.
(algorithms_options): New option --hostkey-algorithm.
(filter_algorithms): New function.
(filter_algorithms_l): New function.

* src/algorithms.c (default_crypto_algorithms): Make the default
list more restrictive.
(all_crypto_algorithms): New function, returning a less
conservative algorithm list.

Rev: src/algorithms.c:1.16
Rev: src/algorithms.h:1.7