[3.1.1] Round up imagecrash support with HTML.MaxImgLength

- Add $max to AttrDef/HTML/Pixels.php
- Add %HTML.MaxImgLength
- CSS width/height allows percents when MaxImgLength is disabled


git-svn-id: http://htmlpurifier.org/svnroot/htmlpurifier/trunk@1762 48356398-32a2-884e-a903-53898d9a118a

library/HTMLPurifier/ConfigSchema/schema/CSS.MaxImgLength.txt

@@ -8,4 +8,8 @@ VERSION: 3.1.1
  effectively the <code>width</code> and <code>height</code> properties.
  Only absolute units of measurement (in, pt, pc, mm, cm) and pixels (px) are allowed. This is
  in place to prevent imagecrash attacks, disable with null at your own risk.
+ This directive is similar to %HTML.MaxImgLength, and both should be
+ concurrently edited, although there are
+ subtle differences in the input format (the CSS max is a number with
+ a unit).
 </p>