merge revisions 2205 and 2206 from trunk to branch-1_7

feature 803: Implement keyboard navigation (left/right arrows) on the picture page
fix: non-image elements without representative and without mime type icon default to thumbnail if possible

git-svn-id: http://piwigo.org/svn/branches/branch-1_7@2207 68402e56-0260-453c-a942-63ccdbb3a9ee

include/functions_picture.inc.php

@@ -149,6 +149,11 @@ function get_image_location($element_info)
       $ext = get_extension($element_info['path']);
       $path = get_themeconf('mime_icon_dir');
       $path.= strtolower($ext).'.png';
+      if ( !file_exists(PHPWG_ROOT_PATH.$path)
+          and !empty($element_info['tn_ext']) )
+      {
+        $path = get_thumbnail_location($element_info);
+      }
     }
 
   // plugins want another location ?