Get rid of implicit declaration of function warning

--- exp_main_sub.c.orig	Thu Sep  9 19:37:20 2010
+++ exp_main_sub.c	Thu Sep  9 19:38:01 2010
@@ -28,6 +28,9 @@
 #include "tcldbg.h"
 #endif
 
+
+extern int exp_tty_cooked_echo(Tcl_Interp *interp, exp_tty *tty_old, int *was_raw, int *was_echo);
+
 #ifndef EXP_VERSION
 #define EXP_VERSION PACKAGE_VERSION
 #endif
