Replace usestrictprivmsg with something actually useful.

Every IRC server we support (other than Bahamut which is probably
on the chopping bock) uses UIDs so this setting does nothing.

Instead, allow configuring a server-side alias for each service
and use that when servicealias is enabled.

data/botserv.example.conf

@@ -59,6 +59,17 @@ service
 	 * Prefixes may be given to the channels in the form of mode characters or prefix symbols.
 	 */
 	#channels = "@#services,#mychan"
+
+	/*
+	 * The server alias that can be used to securely message this service. If
+	 * your IRC server does not have an alias for this service you can set this
+	 * to an empty string to tell users to use /msg instead.
+	 *
+	 * This setting is ignored when options:servicealias is disabled.
+	 *
+	 * Defaults to the nick of the service if not set.
+	 */
+	#alias = "BS"
 }
 
 /*