Remove writable shortcut and errorneous workaround to get [connect -async] fail error to [fconfigure -error]
  *  More test improvements for async sockets.
  *  Advance async connections whenever the channel is touched (e.g. by [chan configure]).
  *  Add a noblock argument to WaitForConnect(), so that advancing async connections from [chan configure] doesn't block even on a blocking socket.
Merge back from fork that happened due to core.tcl.tk outage