A few History tweaks

Retry subscription on error.

Also upgrade uglify-js.

Rework tests that didn’t work when multiple clients run at once.

Remove sessionData.

Add tests to check that account data is cleaned up after a session
closes.

Make `establishConnection` available to account tests.

Remove code duplication between `poll` (now called `simplePoll`) and
the async_multi `pollUntil`.

make connection._oplogHandle into a classy object

Add a comment about no-op changed calls

Revert "Upgrade to SockJS 0.3.8."

This reverts commit 86b978b.

The commit breaks some nuanced node stream issues
that manifest as `meteor test-packages` handing
on Firefox. We'll remember to un-revert this revert
once devel is fixed (with a new release of Node)

extract attribute manager for 'selected' property

Refix issue meteor#770

{{#with falseyValue}} should render {{else}} content