Upgrade to Node 0.10.3.
Upgrade to Underscore 1.4.4.
Improve test driver performance.

Upgrading Underscore to 1.4.4 fixes a bug where _.throttle would sometimes take
double its timeout to deliver calls. So with this bugfix, our test suite
performs worse because reactivity happens more often. Reduce the throttling to
one update of the big table per second instead of twice a second. (Also, there's
no need to defer and call flush; the changed call does that!)
SockJS bug fix.

Ensure that when in livedata_server.js we send version negotiation error and
then close the socket, that the close actually gets delivered. In 0.3.4, this
often caused the livedata tests to spin as the client kept not quite getting the
error and reconnecting.

(Strangely, 0.3.5 on its own seems to fix this. I'm not quite sure why.)
Use npm install --force to get around NPM cache corruption bug.

Initially tried this before the Node upgrade but test_bundler_npm failed
sporadically.