Add support for disabling default SIGINT and EOF behavior.

This patch adds support for `--disable-eof` and `--disable-sigint` to
the Editline configure script.  With either of these two switches the
`tty_special()` function bypasses the special TTY checks making it
possible to bind Ctrl-C and Ctrl-D to custom callbacks.  This can be
useful if you want to emulate a Cisco style CLI rather than traditional
UNIX.

The user can of course also redefine the VINTR and VEOF special terminal
control characters, but these configure script switches may be easier to
use for some.

Also, the CLI example has been updated to bind Ctrl-D, Ctrl-C and Ctrl-Z
for testing purposes.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

src/editline.c

@@ -924,10 +924,12 @@ static el_status_t emacs(int c)
 
 static el_status_t tty_special(int c)
 {
+#ifdef CONFIG_SIGINT
     if (c == rl_intr) {
         el_intr_pending = SIGINT;
         return CSsignal;
     }
+#endif
     if (c == rl_quit) {
         el_intr_pending = SIGQUIT;
         return CSeof;
@@ -953,8 +955,10 @@ static el_status_t tty_special(int c)
         return kill_line();
     }
 
+#ifdef CONFIG_EOF
     if (c == rl_eof && rl_point == 0 && rl_end == 0)
         return CSeof;
+#endif
 
     return CSdispatch;
 }