Alias `queue()` to `push()`

streams2 as a [`push()`][1] that does effectively the same as `queue()`. 

It might be nice to allow `push()` to work on `through` aswell, or if 
we have time we can get @izs to pave the `queue()` cow-path.

  [1]: https://github.com/joyent/node/blob/master/doc/api/stream.markdown#readablepushchunk