Fix building with gcc-4.6

https://bugs.gentoo.org/show_bug.cgi?id=366191

Part of debian patch by Ricardo Mones <mones@debian.org>
Fix invalid conversion and addded Ubuntu patch (thanks Ilya Barygin <barygin@gmail.com>)

--- a/src/preferences.cc
+++ b/src/preferences.cc
@@ -82,8 +82,8 @@
 
 void Preferences :: init (void)
 {
-  ((Size_score)(Preferences :: size_score)).score = 0;
-  ((Size_score)(Preferences :: size_score)).size  = 0;
+  size_score.score = 0;
+  size_score.size  = 0;
 }
   
 void Preferences :: kill (void)