add a bufferevent_setwatermark prototype, so it compiles on OpenBSD fine; small correction in the README

README

@@ -1,10 +1,15 @@
 icbd: a simple yet secure ICB daemon written in C
 =================================================
 
+OS support:
+===========
+
+Currently, server supports OpenBSD/AerieBSD only.
+
 FAQ:
 ====
 
-Q. WTF?
+Q. ICB? WTF?
 A. http://www.icb.net/
 
 Q. Ahoi! Where are the protocol specs?
@@ -13,9 +18,6 @@ A. http://www.icb.net/_jrudd/icb/protocol.html
 Q. This' really old shit, man!
 A. Yes, it is!
 
-Q. Why do you need that shit, man?
-A. Well, I don't need it at all!
-
 Q. Any clients?
 A. There are icb, ircII, irssi (with icb plugin), zenicb (emacs plugin) and
    an irc to icb proxy - icbirc.

icbd.c

@@ -56,6 +56,11 @@ void icbd_grplist(char *);
 void icbd_restrict(void);
 void icbd_write(struct icb_session *, char *, ssize_t);
 
+#ifndef bufferevent_setwatermark
+void bufferevent_setwatermark(struct bufferevent *, short events,
+    size_t lowmark, size_t highmark);
+#endif
+
 int
 main(int argc, char *argv[])
 {