We reported any PROXY connection failure as JUNK. Now we report the same
reasons as for failing HTTP1 connections.

Implmentation:

SES_DeleteHS() asserts that the hs argument be negative (one of
JUNK, CLOSE, TIMEOUT, OVERFLOW, EOF).

HTC_RxStuff() may return OVERFLOW, JUNK, COMPLETE, EOF or TIMEOUT (or,
instead of TIMEOUT, IDLE if the callback returned EMPTY).

Because vpx_complete() only returns JUNK, OVERFLOW or MORE, using
the HTC_RxStuff() return value for SES_DeleteHS() is safe if different
from COMPLETE.