Get rid of implicit declaration of function warning

--- exp_chan.c.orig	Thu Sep  9 19:29:43 2010
+++ exp_chan.c	Thu Sep  9 19:30:27 2010
@@ -37,6 +37,7 @@
 #include "exp_log.h"
 #include "tcldbg.h" /* Dbg_StdinMode */
 
+extern void exp_background_channelhandler(ClientData,int);
 extern int		expSetBlockModeProc _ANSI_ARGS_((int fd, int mode));
 static int		ExpBlockModeProc _ANSI_ARGS_((ClientData instanceData,
 			    int mode));
