Updated WebKit SDK (@r51062)

I have updated the WebKitSDK to correspond to SVN revision r51062.
Edit: I stupidly wrote "-webkit-block-shadow", when I meant "-webkit-box-shadow". Thanks to Brad K. for catching this!
Major changes in this revision:
* Support for -webkit-box-shadow.
* General support for Canvas and SVG shadows in Cairo.
* New SVG filter effects: feComposite, feDisplacementMap, feGaussianBlur, feMorphology
* Many SVG rendering improvements, including support for SourceAlpha.
* Support for CSS in Text Kerning and ligature.
* Ability to specify the number of visible lines in -webkit-line-clamp.
* Implement DOM Level 3 composition events.
* Implement CSSOM Range.getClientRects/getBoundingClientRect.
* @import now works in user stylesheets.
* Protect Canvas methods from NaN and Infinity.
* Web Inspector improvements (see this blog entry for details), but many cool new features!
* Some support for -webkit-color-correction (needs further testing on this platform).
* JavaScript engine speed-ups.
* Initial <ruby> support (see this blog entry for details)
* Accessibility improvements.

Clearly this is a significant amount of new logic, so there may be some regressions. Please let me know if you encounter any problems with this new version.

Unfortunately I have not been able to complete work on 3D CSS or WebGL, but stay tuned!