two new test for send callback
two new test for send callback

in this new tests we assert that:
1- when socket get closed and one or more packet(s) are in writeBuffer,
callback references get cleaned to avoid memory leak.
2- callbacks still execute in polling mode

kapouer/engine.io,socketio/engine.io,nkzawa/engine.io,CantemoInternal/engine.io,socketio/engine.io