[1.4.0] CSS property background-position implemented. Also:

- Fixed some misinformation in Percentage
- Add support for lowercase CSS length units

git-svn-id: http://htmlpurifier.org/svnroot/htmlpurifier/trunk@661 48356398-32a2-884e-a903-53898d9a118a

library/HTMLPurifier/CSSDefinition.php

@@ -79,6 +79,7 @@ class HTMLPurifier_CSSDefinition
         $this->info['background-attachment'] = new HTMLPurifier_AttrDef_Enum(
             array('scroll', 'fixed')
         );
+        $this->info['background-position'] = new HTMLPurifier_AttrDef_BackgroundPosition();
         
         // pending its own validator as a shorthand
         $this->info['background'] =