Fix recognizing the default (empty) locale as English

This fixes selecting the right man page for 'mount', which would
otherwise grab a version from an old distro that happened to have it
with an explicit 'en' locale.

sql/schema.sql

@@ -103,7 +103,7 @@ $$ LANGUAGE SQL IMMUTABLE;
 
 
 CREATE OR REPLACE FUNCTION is_english_locale(locale text) RETURNS bool AS $$
-  SELECT locale IS NULL OR locale LIKE 'en%';
+  SELECT locale IS NULL OR locale = '' OR locale LIKE 'en%';
 $$ IMMUTABLE LANGUAGE SQL;