tests: fix compilation on OSX (libargp detection)
Added known host test cases
known_hosts: add ssh_knownhosts_algorithms()

Goal of that function is to test the preferred key exchange methods
based on what's available in the known_hosts file
knownhosts: add test case for bug #138
Knownhosts: implement hostkey with knownhosts heuristic
server: allow custom server banners (bug #83)