Minimize Redis connection shadowing

[JakeCooper]

Use <-done at the end of incomingTxWatcher to block variables from losing scope. Also add the defer call there too.

Issue being that the L15 of incomingTxWatcher could shadow a variable used somewhere else.

[trstephen]

I thought about it and I'm not sure we need to use <-done to maintain scope. handler should be the one responsible for getting a redis connection from the pool.

1. Pools (mostly) eliminate the connection setup overhead by re-using idle connections
2. If you have a single connection for all of incomingTxWatcher does that mean each instance of handler will try to use the same connection? It seems like danger lies ahead if we use a single connection.