Added export SVG test spec

Had to change the way the new window was opened. It now opens to a blank
page and the SVG gets written to it as an img element after the window
is opened. I had to do this because I couldn't access the window's
elements when it had a data URI since it was a different protocol than
http and Chrome complained about protocol mismatch. Now they're both
http.
Removed new window default body margin of 8 pixels
Added popup blocked question to error message
Merge pull request #99 from tranek/develop

Added Export SVG test spec