Cleanup: SBuf report how many bytes consume()d
Bug 4065: round-robin neighbor selection with unequal weights
"ssl_bump none" mode crashes squid

After r13324 patch the SBuf argument of the ConnStateData::handleReadData member
is used only to check if ConnStateData::In::buf is correctly filled with read
data. ConnStateData::handleReadData considers that the data already written
in ConnStateData::in.buf and checks if the passed Sbuf argument is the
ConnStateData::in.buf:

bool ConnStateData::handleReadData(SBuf *buf)
{
   assert(buf == &in.buf);
   .....

The httpsSslBumpAccessCheckDone function needs to write the CONNECT request 
generated internally to force tunnel mode, in ConnStateData::In::buf and then
call ConnStateData::handleReadData method.
Docs: mention -k restart in command line usage
Cleanup: drop Auth::User::proxy_auth_list header cache

This list/cache was originally used to short-circuit auth helper lookups
based on previousy seen [Proxy-]Authorization header strings.
However, that permitted replay attacks in most auth schemes and has been
replaced by scheme-specific mechanisms:

* Basic and Digest credentials are cached in the global user name cache
  wih additional nonce/password comparisons to verify located entries.

* NTLM and Negotiate credentials are cached in the ConnStateData with
  exact-match comparison done to verify tokens.
Cleanup: document and rename Auth::UserRequest::module_start to startHelperLookup
Bug 4056: assertion MemPools[type] from netdbExchangeStart()