Added page.clipRect for rasterizing via PhantomJS

[jkphl]

This might be an issue specific for my platform (running on Node.js v5.10.1 on a Gentoo box), but I need to have settings for page.clipRect (docs here) in place as well (alongside with page.viewportSize) to make the rendered PNG have the correct dimensions. If clipRect is missing, there will always be PhantomJS' default dimensions (400 x 300 px) kicking in for the sides being less than these defaults. I.e. an SVG supposed to render as 500 x 100 px will end up being 500 x 300 px, and a 100 x 500 px one will end up with 400 x 500 px. The page.clipRect might not be necessary for other platforms, but I don't see any harm for them either.

[jkphl]

Secondly, PhantomJS obviously has got some problems with SVG files containing CSS media queries (see mediaqueries.svg.txt as an example; had to give it a .txt ending for upload). It looks like setting the page dimensions after the SVG has been loaded won't trigger PhantomJS to properly re-render the viewport and reflect the changes caused by the media queries. Forcing PhantomJS to reload the SVG once more after setting the dimensions seems to solve this problem.

[domenic]

I'm taking the first commit. I can't take the second without a test; what is the expected rendering of mediaqueries.svg?

[jkphl]

@domenic When you open mediaqueries.svg in your browser and resize the window, the color of the zebra should change depending on the window width (there are 3 color variants). I don't remember the exact situation, but normally PhantomJS should render the the file at its original size, which means that the zebra should be red. It wasn't, however, because PhantomJS seemed to apply the size shortly after exporting the binary data.

[domenic]

Thanks. It looks like this already works, so I committed some tests to make sure it stays that way.