restore PROXY protocol support

support for PROXY was removed in 43e28e2fef. After discussion,
it's worth keeping around in case of client compatibility issues,
and until /rehash support is more mature.

irc/help.go

@@ -356,6 +356,13 @@ Replies to a PING. Used to check link connectivity.`,
 		text: `PRIVMSG <target>{,<target>} <text to be sent>
 
 Sends the text to the given targets as a PRIVMSG.`,
+	},
+	"proxy": {
+		oper: true, // not really, but it's restricted anyways
+		text: `PROXY TCP4/6 <sourceip> <destip> <sourceport> <destport>
+
+Used by haproxy's PROXY protocol, to allow for alternate TLS support:
+http://www.haproxy.org/download/1.7/doc/proxy-protocol.txt`,
 	},
 	"rename": {
 		text: `RENAME <channel> <newname> [<reason>]