Fix for mkconfig to be able to handle empty continued lines.
Patch from [ruby-core:20420] via bug 234877.

--- mkconfig.rb.orig	2008-06-08 01:37:10.000000000 +0900
+++ mkconfig.rb	2009-02-12 13:39:02.000000000 +0900
@@ -54,7 +54,7 @@
       continued_name = name
       next
     end
-  when /^"(.+)"\s*(\\)?$/
+  when /^"(.*)"\s*(\\)?$/
     if continued_line
       continued_line <<  $1
       unless $2