add more SVG tags to dom.clj

[osnr]

React 0.9 added some new tags:

Added support for SVG tags defs, linearGradient, polygon, radialGradient, stop

http://facebook.github.io/react/blog/2014/02/20/react-v0.9.html

Would be great to get support for these so we can add marker arrows, etc.

[osnr]

(turns out this isn't especially useful [for me] because React itself doesn't support marker and some other tags)

[piranha]

Contributing those to React shouldn't be hard if you need them. :)

[osnr]

You'd be surprised; there are still a few standing pull requests to add SVG tags:
facebook/react#868
facebook/react#938 (this one has the tags I need, but it's huge)
facebook/react#1032

This smaller one was actually closed in favor of 938, which seems like a mess to wade into: facebook/react#830

But this is off-topic, anyway. Still would be good to add these tags to Om that are already supported in React 0.9.

[swannodette]

fixed 264418b