* lib/irb/workspace.rb: fix BUG#4793.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@32252 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,7 @@
+Tue Jun 28 00:08:43 2011  Keiju Ishitsuka  <keiju@ishitsuka.com>
+
+	* lib/irb/workspace.rb: fix BUG#4793.
+
 Mon Jun 27 22:06:12 2011  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
 
 	* thread_pthread.c (consume_communication_pipe): don't use C99

lib/irb/workspace.rb

@@ -97,7 +97,7 @@ EOF
       when 3
 	return nil if bt =~ /irb\/.*\.rb/
 	return nil if bt =~ /irb\.rb/
-	bt.sub!(/:\s*in `irb_binding'/, '')
+	bt = bt.sub(/:\s*in `irb_binding'/, '')
       end
       bt
     end