(Fbacktrace): Don't overwrite print-level on exit.

Also only override Vprint_level if it isn't already bound, and
increase the level to 8 to produce more useful backtraces for bug
reports.

src/ChangeLog

+2010-09-30  Lars Magne Ingebrigtsen  <larsi@gnus.org>
+
+	* eval.c (Fbacktrace): Don't overwrite print-level on exit.  Also
+	only override Vprint_level if it isn't already bound, and increase
+	the level to 8 to produce more useful backtraces for bug reports.
+
 2010-09-30  Dan Nicolaescu  <dann@ics.uci.edu>
 	* Makefile.in: ecrt0.c does not exist anymore, do not mention it.

src/eval.c

@@ -3441,8 +3441,10 @@ Output stream used is value of `standard-output'.  */)
   Lisp_Object tail;
   Lisp_Object tem;
   struct gcpro gcpro1;
+  Lisp_Object old_print_level = Vprint_level;
 
-  XSETFASTINT (Vprint_level, 3);
+  if (NILP (Vprint_level))
+    XSETFASTINT (Vprint_level, 8);
 
   tail = Qnil;
   GCPRO1 (tail);
@@ -3483,7 +3485,7 @@ Output stream used is value of `standard-output'.  */)
       backlist = backlist->next;
     }
 
-  Vprint_level = Qnil;
+  Vprint_level = old_print_level;
   UNGCPRO;
   return Qnil;
 }