From http://ftp.gnu.org/pub/gnu/readline/readline-6.3-patches/readline63-007

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>

			   READLINE PATCH REPORT
			   =====================

Readline-Release: 6.3
Patch-ID: readline63-007

Bug-Reported-by:	John Lenton
Bug-Reference-ID:
Bug-Reference-URL:	https://bugs.launchpad.net/ubuntu/+source/bash/+bug/1317476

Bug-Description:

Readline should allow SIGALRM and SIGVTALRM (if available) to `interrupt'
rl_getc and cause the handler to run when not in a signal handling context.

Patch (apply with `patch -p0'):

*** a/readline-6.3-patched/input.c	2014-01-10 15:07:08.000000000 -0500
--- b/input.c	2014-05-30 16:20:56.000000000 -0400
***************
*** 535,540 ****
--- 538,551 ----
        else if (_rl_caught_signal == SIGHUP || _rl_caught_signal == SIGTERM)
  	return (RL_ISSTATE (RL_STATE_READCMD) ? READERR : EOF);
+       /* keyboard-generated signals of interest */
        else if (_rl_caught_signal == SIGINT || _rl_caught_signal == SIGQUIT)
          RL_CHECK_SIGNALS ();
+       /* non-keyboard-generated signals of interest */
+       else if (_rl_caught_signal == SIGALRM
+ #if defined (SIGVTALRM)
+ 		|| _rl_caught_signal == SIGVTALRM
+ #endif
+ 	      )
+         RL_CHECK_SIGNALS ();
  
        if (rl_signal_event_hook)
*** a/readline-6.3/patchlevel	2013-11-15 08:11:11.000000000 -0500
--- b/patchlevel	2014-03-21 08:28:40.000000000 -0400
***************
*** 1,3 ****
  # Do not edit -- exists only for use by patch
  
! 6
--- 1,3 ----
  # Do not edit -- exists only for use by patch
  
! 7