Fix two bugs with caching of customized raw definitions.

The first bug is that we will repeatedly write out the result
of a customized raw definition to the filesystem, even when a cache
entry already exists.

The second bug is that caching these definitions doesn't actually
work (the cache entry is written but never used.)  A new API
for retrieving raw definitions permits the user to take advantage
of caching.

Signed-off-by: Edward Z. Yang <ezyang@mit.edu>

library/HTMLPurifier/Definition.php

@@ -12,6 +12,17 @@ abstract class HTMLPurifier_Definition
      */
     public $setup = false;
 
+    /**
+     * If true, write out the final definition object to the cache after
+     * setup.  This will be true only if all invocations to get a raw
+     * definition object are also optimized.  This does not cause file
+     * system thrashing because on subsequent calls the cached object
+     * is used and any writes to the raw definition object are short
+     * circuited.  See enduser-customize.html for the high-level
+     * picture.
+     */
+    public $optimized = null;
+
     /**
      * What type of definition is it?
      */