Import github.com/gorilla/websocket into third_party at its 2119675aadf

Change-Id: Id3d62b16d3c0186295559205b86c40b95881d0d0
Start of Camlistore WebSocket support, for showing live search queries in the UI.

If the JavaScript UI is open and the query you're looking at changes
due to new data arriving, the server should push the update search
results to you live, without needing to poll.

Change-Id: I00faf7737f9a459de39b21fb5226a8000feeee2b