Fixes: http://bugs.webkit.org/show_bug.cgi?id=17258 (SVG uses erroneous cursor implementation)

SVG cursors are not well-integrated within the CSS(3) cursor support in WebCore.
SVGCursorElement duplicates CSSCursorImageValue functionality and inherits from
CachedResourceClient itself, handling remote-image acquisation on its own.

RenderStyle's CursorData class holds "IntPoint hotSpot", "CachedImage* image"
and just for SVG a 'String cursorFragmentId' (a reference to a SVG <cursor> element, by id).

SVG stores a reference to a SVGCursorElement, which holds a CachedImage pointer itself -
instead of storing the CachedImage in the CursorData class, as it's supposed to be.
Because of that several places in WebCore contain special SVG cursor handling - which
is unneeded.

Fix all issues by integrating within CSSCursorImageValue, remove 'String cursorFragmentId'
from RenderStyle, kill any special SVG cursor handling in WebCore and fix dynamic attribute
changes through DOM / SVG DOM (scripting of 'x' / 'y' / 'xlink:href' attribute).


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@30208 268f45cc-cd09-0410-ab3c-d52691b4dbfc