Added %Core.RemoveProcessingInstructions.

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

library/HTMLPurifier/ConfigSchema/schema/Core.RemoveProcessingInstructions.txt

@@ -0,0 +1,11 @@
+Core.RemoveProcessingInstructions
+TYPE: bool
+VERSION: 4.1.2
+DEFAULT: false
+--DESCRIPTION--
+Instead of escaping processing instructions in the form <code>&lt;? ...
+?&gt;</code>, remove it out-right.  This may be useful if the HTML
+you are validating contains XML processing instruction gunk, however,
+it can also be user-unfriendly for people attempting to post PHP
+snippets.
+--# vim: et sw=4 sts=4

library/HTMLPurifier/Lexer.php

@@ -297,6 +297,11 @@ class HTMLPurifier_Lexer
         // represent non-SGML characters (horror, horror!)
         $html = HTMLPurifier_Encoder::cleanUTF8($html);
 
+        // if processing instructions are to removed, remove them now
+        if ($config->get('Core.RemoveProcessingInstructions')) {
+            $html = preg_replace('#<\?.+?\?>#s', '', $html);
+        }
+
         return $html;
     }