Fixed assertion related to TCP_RESET feature

Fixed assertion related to TCP_RESET feature

When 'deny_info TCP_RESET' was used (and triggered), Squid asserted
in connNoteUseOfBuffer().  Because we called comm_reset_close() in
clientReplyContext::sendMoreData(), the ClientHttpRequest was freed
before http->doCallouts() returned.  Thus we were accessing freed
memory and passing a bad value to connNoteUseOfBuffer().

I've moved the comm_reset_close() call from there to
clientProcessRequest().  I dont really like having it in
clientProcessRequest(), but it seems to be the only place that will
work.  At least this way we can avoid the destroying ClientHttpRequest
before clientProcessRequest() reaches 'finish'.