Simpler to drop http.HTTPClient where not needed and minor edits
C style casts for consistency
Fix crash if INKVConnInternal::do_io_close() gets called after a message is already complete
Send our own TS_EVENT_VCONN_WRITE_COMPLETE event upstream when the input is complete otherwise HttpSM::update_stats() won't get called and the transaction won't get logged.  (If there are upstream transformations they won't get a chance to clean up otherwise!)
Improve comments