Initiate /start request after a transport is selected in the JS client

- This is how the .NET client already behaves

#3104
Bump version to 2.1.1
.NET Client: Dispatch failed hub invocation callbacks on reconnecting
- #3101
Respond to JSONP send requests with the correct MIME type

#3110
Rewrite ProcessStartRequests to not use async/await to avoid deadlocks

- Deadlocks would occur in the old async/await code if someone attached
  to the PreSendRequestHeaders event.

#3116
Attach to the PreSendRequestHeaders event for only one test
Bump the ConnectionsDisconnected PC even when OnDisconnected throws
Removed the old OnDisonnected overload

- Removing the old overload is preferable to changing its behavior

#3115
Merge branch 'release'
Merge pull request #1 from SignalR/master

pull request on signalr