Fixes language switch for overview layouts

See scala#129

Author: eed3si9n

_layouts/overview.html

@@ -9,6 +9,12 @@
 
     <div class="span10">{% if page.title %}<h1>{{ page.title }}</h1>{% else %}<h1>{{ site.title }}</h1>{% endif %}</div>
 
+    {% for pg in site.posts %}
+      {% if pg.overview == page.overview and pg.languages %}
+        {% assign languages = pg.languages %}
+      {% endif %}
+    {% endfor %}
+
     {% for pg in site.pages %}
       {% if pg.overview == page.overview and pg.languages %}
         {% assign languages = pg.languages %}

overviews/core/_posts/2010-09-07-collections.md

@@ -4,4 +4,5 @@ title: Scala's Collections Library
 disqus: true
 partof: collections
 overview: collections
+languages: [ja]
 ---

overviews/core/_posts/2010-11-30-actors.md

@@ -2,6 +2,7 @@
 layout: overview
 title: The Scala Actors API
 overview: actors
+languages: [es]
 ---
 
 **Philipp Haller and Stephen Tu**

overviews/core/_posts/2012-03-27-parallel-collections.md

@@ -4,4 +4,5 @@ title: Scala's Parallel Collections Library
 disqus: true
 partof: parallel-collections
 overview: parallel-collections
+languages: [es, ja]
 ---

overviews/core/_posts/2012-09-20-futures.md

@@ -4,6 +4,7 @@ title: Futures and Promises
 label-color: success
 label-text: New in 2.10
 overview: futures
+languages: [ja]
 ---
 
 **By: Philipp Haller, Aleksandar Prokopec, Heather Miller, Viktor Klang, Roland Kuhn, and Vojin Jovanovic**

overviews/core/_posts/2012-09-21-string-interpolation.md

@@ -5,6 +5,7 @@ disqus: true
 label-color: success
 label-text: New in 2.10
 overview: string-interpolation
+languages: [es, ja]
 ---
 
 **Josh Suereth**

overviews/core/_posts/2012-11-03-value-classes.md

@@ -4,6 +4,7 @@ title: Value Classes and Universal Traits
 label-color: success
 label-text: New in 2.10
 overview: value-classes
+languages: [ja]
 ---
 
 **Mark Harrah**