Document -trusted_first option in man pages and help.

Add -trusted_first description to help messages and man pages
of tools that deal with certificate verification.

doc/apps/s_server.pod

@@ -34,6 +34,7 @@ B<openssl> B<s_server>
 [B<-state>]
 [B<-CApath directory>]
 [B<-CAfile filename>]
+[B<-trusted_first>]
 [B<-nocert>]
 [B<-cipher cipherlist>]
 [B<-quiet>]
@@ -183,6 +184,11 @@ and to use when attempting to build the server certificate chain. The list
 is also used in the list of acceptable client CAs passed to the client when
 a certificate is requested.
 
+=item B<-trusted_first>
+
+Set certificate verification option.
+See the L<B<verify>|verify(1)> manual page for details.
+
 =item B<-state>
 
 prints out the SSL session states.