Improve error messages for incorrect use of socket interface

[DartBot]

This issue was originally filed by @financecoding

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What steps will reproduce the problem?

1. The following url tells more about the bug https://gist.github.com/2188456
2. git clone git://gist.github.com/2188456.git
3. cd 2188456
4. dart socketTest.dart

What is the expected output? What do you see instead?
Exceptions being thrown cause _SocketBase._id is -1. In earlier sdk this did not happen, _id would be set to 0 if the socket was created successfully.

What version of the product are you using? On what operating system?
Information provided in the gist

Please provide any additional information below.
Dart Rocks!

[sgjesse]

There have been recent changes to make the actual connecting of the socket asynchronous. That is the actual connetion will not be present until the onConnect callback is called. Likewise errors are handled using the onError callback which should now provide an Exception object with information on the actual error.

The motivation for this is:

1. DNS lookup can taks several hundred milliseconds, and we don't want to block in the IO code
2. Be consistent with the asynchronous programming model

Try to rewrite the code to:

main() {
  Socket s = new Socket("127.0.0.1", 8888);
  s.onError = (e) => print("Error: $e");
  s.onConnect = () {
    print('s = ${s.available()}');
    s.close();
  }
}

The SocketIOException thrown has the message "SocketIOException: Error: available failed - invalid socket handle". That is not very informative. Something like "SocketIOException: Error: available failed - socket connection pending". To handle this a socket should have a state CONNECTING, CONNECTED, CLOSED_READ, CLOSED_WRITE, CLOSED.

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Set owner to @sgjesse.
Removed Type-Defect label.
Added Type-Enhancement, Area-IO, Accepted labels.

[madsager]

Changed the title to: "Improve error messages for incorrect use of socket interface".

[madsager]

Added this to the M1 milestone.

[madsager]

Removed this from the M1 milestone.

[sgjesse]

Added AssumedStale label.

[kevmoo]

Removed Area-IO label.
Added Area-Library, Library-IO labels.