FALLBACK updates

Correct version and add a note about default.

Author: geographika

en/mapfile/class.txt

@@ -97,11 +97,11 @@ EXPRESSION [string]
    :name: mapfile-class-fallback
 
 FALLBACK [true|false]
-    Specifies whether the class should act as a fallback class.
-    A fallback class is applied if and only if none of the previously 
+    Specifies whether the class should act as a fallback class. Default is false.
+    A fallback class is applied if and only if none of the previously
     defined classes has been applied. This is similar in concept to
     the :ref:`sld` ElseFilter.
-   .. versionadded:: 8.5
+   .. versionadded:: 8.6
 
 .. index::
    pair: CLASS; GROUP