BUG/MINOR: http: don't report server aborts as client aborts

BUG/MINOR: http: don't report server aborts as client aborts

Commit f003d37 ("BUG/MINOR: http: don't report client aborts as server errors")
attempted to fix a longstanding issue by which some client aborts could be
logged as server errors. Unfortunately, one of the tests involved there also
catches truncated server responses, which are reported as client aborts.

Instead, only check that the client has really closed using the abortonclose
option, just as in done in the request path (which means that the close was
propagated to the server).

The faulty fix above was introduced in 1.5-dev15, and was backported into
1.4.23.

Thanks to Patrick Hemmer for reporting this issue with traces showing the
root cause of the problem.