More doc for debug-on-event.

* emacs/trouble.texi (Checklist): Mention debug-on-event.

* lispref/debugging.texi (Error Debugging): Mention debug-on-event default.

doc/emacs/ChangeLog

 2012-02-05  Glenn Morris  <rgm@gnu.org>
 
+	* trouble.texi (Checklist): Mention debug-on-event.
+
 	* maintaining.texi (Maintaining): Add cross-ref to ERT.
 
 2012-02-04  Glenn Morris  <rgm@gnu.org>

doc/emacs/trouble.texi

@@ -784,6 +784,12 @@ non-@code{nil} will start the Lisp debugger and show a backtrace.
 This backtrace is useful for debugging such long loops, so if you can
 produce it, copy it into the bug report.
 
+@vindex debug-on-event
+If you cannot get Emacs to respond to @kbd{C-g} (e.g., because
+@code{inhibit-quit} is set), then you can try sending the signal
+specified by @code{debug-on-event} (default SIGUSR2) from outside
+Emacs to cause it to enter the debugger.
+
 @item
 Check whether any programs you have loaded into the Lisp world,
 including your initialization file, set any variables that may affect

doc/lispref/ChangeLog

+2012-02-05  Glenn Morris  <rgm@gnu.org>
+
+	* debugging.texi (Error Debugging): Mention debug-on-event default.
+
 2012-02-04  Glenn Morris  <rgm@gnu.org>
 
 	* backups.texi (Reverting): Mention revert-buffer-in-progress-p.

doc/lispref/debugging.texi

@@ -153,8 +153,8 @@ If you set @code{debug-on-event} to a special event (@pxref{Special
 Events}), Emacs will try to enter the debugger as soon as it receives
 this event, bypassing @code{special-event-map}.  At present, the only
 supported values correspond to the signals @code{SIGUSR1} and
-@code{SIGUSR2}.  This can be helpful when @code{inhibit-quit} is set
-and Emacs is not otherwise responding.
+@code{SIGUSR2} (this is the default).  This can be helpful when
+@code{inhibit-quit} is set and Emacs is not otherwise responding.
 @end defopt
 
   To debug an error that happens during loading of the init