merged IE10 pong fix from jmatthewsr-ms

Because the socket.io guys don't care much about merging fixes to the currently used stable version, I have to fork and merge the fix myself. Fix comes from here: https://github.com/jmatthewsr-ms/socket.io/commit/32a44a3b5dcc2d0484fd7359c27db95f3a2d053a