wrong font-size calculations in css.el and font.el

The function css-expand-length does not take the default character size
in pixels into account when calculating em and ex values. This results
typically in values very much too large.

I would like to suggest using something like the following in the
condition branch that deals with em and ex values:

    (round (font-spatial-to-canonical
            (concat (number-to-string
                     (* (string-to-number (match-string 1 spec))
                        (if height (frame-char-height) (frame-char-width))))
                    "px")))

I don't know if it is advisable to use font-spatial-to-canonical. But
it could be used in other places in this function too.

By the way, this function font-spatial-to-canonical has another bug:
Pixel values are calculated with

	(setq retval (* num (/ pix-width mm-width) (/ 25.4 72.0))))

instead of the correct

	(setq retval (* num (/ mm-width pix-width) (/ 72.0 25.4))))

i.e., exactly the other way round with respect to dividing and
multiplying.

--

-- 
Klaus Straubinger