Build three tiny shared libraries that export the real_gamemode_* symbols
(complete, without real_gamemode_request_end, without
real_gamemode_error_string) and drive the client through them, so no
daemon is needed. Check a missing library, a fall back to the second
library name, request and release once each, a refusal with the library's
reason, a failing release, a missing symbol and a session over the client.
