Correctly detect when SSL subsystem must be initialized

This patch introduces the new function Conf_SSLInUse() to check when the
current server configuration requires the SSL subsystem to be initialized
and accounts incoming as well as outgoing connections -- so this fixes
commit bb20aeb9 ("Initialize SSL when needed only, and disable SSL on
errors") which only handled the inbound case  ...

Tested-by: Brett Smith <brett@w3.org>