generate_translations: do not include some descriptions more than once

By no longer using s.source in the GROUP BY clause, identical
descriptions for binary packages built by more than one source
no longer appear multiple times in Translation-en.

Bug: http://bugs.debian.org/660543

dak/generate_packages_sources2.py

@@ -273,8 +273,8 @@ FROM binaries b
   JOIN source s ON b.source = s.id
 
 WHERE ba.suite = :suite AND o.component = :component
-GROUP BY s.source, b.package, bm_description_md5.value, bm_description.value
-ORDER BY s.source, b.package, bm_description_md5.value
+GROUP BY b.package, bm_description_md5.value, bm_description.value
+ORDER BY MIN(s.source), b.package, bm_description_md5.value
 """
 
 def generate_translations(suite_id, component_id):