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>

configure

@@ -764,6 +764,8 @@ enable_libtool_lock
 enable_unique_history
 enable_default_complete
 enable_arrow_keys
+enable_eof
+enable_sigint
 enable_sigstop
 enable_terminal_bell
 enable_termcap
@@ -1410,7 +1412,9 @@ Optional Features:
   --disable-default-complete
                           Disable default (filename) completion handler.
   --disable-arrow-keys    Disable ANSI arrow keys.
-  --enable-sigstop        Enable SIGSTOP key.
+  --disable-eof           Disable default EOF (Ctrl-D) behavior.
+  --disable-sigint        Disable default SIGINT (Ctrl-C) behavior.
+  --enable-sigstop        Enable SIGSTOP (Ctrl-Z) behavior.
   --enable-terminal-bell  Enable terminal bell on completion.
   --enable-termcap        Use termcap library to query terminal size.
 
@@ -12043,6 +12047,26 @@ $as_echo "#define CONFIG_ANSI_ARROWS 1" >>confdefs.h
 fi
 
 
+# Check whether --enable-eof was given.
+if test "${enable_eof+set}" = set; then :
+  enableval=$enable_eof;
+else
+
+$as_echo "#define CONFIG_EOF 1" >>confdefs.h
+
+fi
+
+
+# Check whether --enable-sigint was given.
+if test "${enable_sigint+set}" = set; then :
+  enableval=$enable_sigint;
+else
+
+$as_echo "#define CONFIG_SIGINT 1" >>confdefs.h
+
+fi
+
+
 # Check whether --enable-sigstop was given.
 if test "${enable_sigstop+set}" = set; then :
   enableval=$enable_sigstop;