Fix bug 973: getComputedStyle does not accept empty string as 2nd arg

I just updated the domita taming to recognize the empty string as legit.
From the bug:

window.getComputedStyle(document.body, null).width; // works
window.getComputedStyle(document.body, '').width; // fails as "Bad pseudo 
class"

Technically caja is right per the spec:

"pseudoElt of type DOMString
The pseudo-element or null if none."


http://www.w3.org/TR/DOM-Level-2-Style/css.html#CSS-OverrideAndComputed

But Mozilla docs contradict this:
"pseudoElt is a string specifying the pseudo-element to match. Should be 
an empty string for regular elements."
https://developer.mozilla.org/En/DOM:window.getComputedStyle

However, all browsers that implement computedStyle accept either form (and 
possibly other falsey values).

[metaweta, 2009-01-27 20:29:15]

LGTM