Async connect on windows hangs in case of failure

[kristjanvalur]

The api uses un-supported patterns when performing non-blocking connect(), which causes Windows to hang.
see PR #930

[kristjanvalur]

Clarification:
A non-blocking connect() call should not be simply "retried". Rather, if the error is EINPROGRESS, the success of the connect whould then be polled with a getsocopt(). The PR explains this in deail and how the approach (retry) which works in practice on linux is not the posix way, and definitely does not work on windows.

This is testable on windows but a bit tricky. The requirement is to have the connect fail, not by a connection refused, but by not getting any response. This is possible, for example, by unplugging the server for a short while.

Without the fix mentioned in the defect, a windows machine will be unable to either succeed of fail on windows, if the initial connect does not immediately succeed or fail.

A previous defect, #817 was closed, with reference to this PR and issue.

[kristjanvalur]

PR #930 was closed, with the changes merged in pr #1073