Fixes to eventhandler and HTTP

Fixes to eventhandler and HTTP

1. Improve error handling in Windows event handler

Whenever an error happens on an IO operation this
generates an error event and the handle is marked as having has
an error.

The test http_shutdown_test have been fixed to check for error as well
as succesful request when the server is closing the connection due to
closing the output stream before the input have been read. The test
have also been extended to have the client send more request data to
get more errors.

2. Disable event handler events until re-enabled from Dart

When an eventhandle event is posted to Dart this event is now
disabled in the eventhandler until re-enabled from Dart.

On Linux and Mac OS this was already the case as the file
descriptor for which the event(s) was posted was removed from
epoll/kqueue when events was posted.

On Windows this is now changed so that after an event is posted
it needs to be re-enabled from Dart code like on Linux and Mac
OS.

Changed the Dart event handler code to avoid posting disabling of
the out handler as the C++ code is already doing this on all
platforms.

3. Cancel HTTP parser when a connection is closing

When a HTTP connection is closing and moved to the close queue
there should be no more envents from the HTTP parser for whatever
data is still buffered.

R=ager@google.com

BUG=7294
Committed: https://code.google.com/p/dart/source/detail?r=16252

[Mads Ager (google), 2012-12-18 11:48:47]

LGTM