This adds a 'ca_file' config option that points to a local
CA cert that will be used to verify certs provided by
connecting clients. The 'ca_file' option is only used if the
server is already properly configured to to use SSL - that
means having a valid 'cert_file' and 'key_file'. If no 'ca_file'
is provided, the behavior will remain the same - the server
will still provide its cert to clients, but it will ignore
certs sent back from those clients.
Fixes bug 1032451
Change-Id: Ie48646b0fc5398ba7cda2fb627b820f533482e00
006254c505