[3.1.2] Add %Output.SortAttr to deal with FCKeditor bug

If %Output.SortAttr is true, attributes are sorted to be
in alphabetical order. This was requested by frank farmer.

See also: http://htmlpurifier.org/phorum/read.php?2,1576

Signed-off-by: Edward Z. Yang <edwardzyang@thewritingpot.com>

library/HTMLPurifier/ConfigSchema/schema/Output.SortAttr.txt

@@ -0,0 +1,13 @@
+Output.SortAttr
+TYPE: bool
+VERSION: 3.1.2
+DEFAULT: false
+--DESCRIPTION--
+<p>
+  If true, HTML Purifier will sort attributes by name before writing them back
+  to the document, converting a tag like: <code>&lt;el b="" a="" c="" /&gt;</code>
+  to <code>&lt;el a="" b="" c="" /&gt;</code>. This is a workaround for
+  a bug in FCKeditor which causes it to swap attributes order, adding noise
+  to text diffs. If you're not seeing this bug, chances are, you don't need
+  this directive.
+</p>

library/HTMLPurifier/Generator.php

@@ -26,6 +26,11 @@ class HTMLPurifier_Generator
      */
     private $_def;
     
+    /**
+     * Cache of %Output.SortAttr
+     */
+    private $_sortAttr;
+    
     /**
      * Configuration for the generator
      */
@@ -38,6 +43,7 @@ class HTMLPurifier_Generator
     public function __construct($config, $context) {
         $this->config = $config;
         $this->_scriptFix = $config->get('Output', 'CommentScriptContents');
+        $this->_sortAttr = $config->get('Output', 'SortAttr');
         $this->_def = $config->getHTMLDefinition();
         $this->_xhtml = $this->_def->doctype->xml;
     }
@@ -142,6 +148,7 @@ class HTMLPurifier_Generator
      */
     public function generateAttributes($assoc_array_of_attributes, $element = false) {
         $html = '';
+        if ($this->_sortAttr) ksort($assoc_array_of_attributes);
         foreach ($assoc_array_of_attributes as $key => $value) {
             if (!$this->_xhtml) {
                 // Remove namespaced attributes