Added Export SVG test spec

Make sure that you allow popups for the site or it may fail the test - seemed to happen in FireFox, but Chrome worked anyway when blocked.

I had to change the popup to point to a blank page that then gets an img element with the src pointing to the data URI written to it instead of pointing the new window directly to the data URI. Chrome complained about the mismatch between http and data URI protocols when trying to read the new window's DOM to verify the SVG. Functionality it should be exactly the same to the end user as it was before.

Addresses issue #93.