Reviewed by eseidel.

        - Fixing http://bugzilla.opendarwin.org/show_bug.cgi?id=6942
          Implement support for "em" and "ex" relative lengths.

        - Layout tests changes:
            Fixed: svg/W3C-SVG-1.1/coords-units-03-b.svg
            New:   svg/custom/coords-relative-units-transforms.svg


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@12764 268f45cc-cd09-0410-ab3c-d52691b4dbfc