Fix %>ru logging of huge URLs (#259)

Fix %>ru logging of huge URLs (#259)

When dealing with an HTTP request header that Squid can parse but that
contains request URI length exceeding the 8K limit, Squid should log the
URL (prefix) instead of a dash. Logging the URL helps with triaging
these unusual requests. The older %ru (LFT_REQUEST_URI) was already
logging these huge URLs, but %>ru (LFT_CLIENT_REQ_URI) was logging a
dash. Now both log the URL (or its prefix).

As a side effect, %>ru now also logs error:request-too-large,
error:transaction-end-before-headers and other Squid-specific
pseudo-URLs, as appropriate.

Also refactored request- and URI-recording code to reduce chances of
similar inconsistencies reappearing in the future.

Also, honor strip_query_terms in %ru for large URLs. Not stripping query
string in %ru was a security problem.

Also fixed a bug with "redirected" flag calculation in
ClientHttpRequest::handleAdaptedHeader(). In general, http->url and
request->url should not be compared directly, because the latter always
passes through uri_whitespace cleanup, while the former does not.

Also fixed a bug with possibly wrong %ru after redirection:
ClientHttpRequest::log_uri was not updated in this case.

Also initialize AccessLogEntry::request and AccessLogEntry::notes ASAP.
Before this change, these fields were initialized in
ClientHttpRequest::doCallouts(). It is better to initialize them just
after the request object is created so that ACLs, running before
doCallouts(), could have them at hand. There are at least three such
ACLs: force_request_body_continuation, spoof_client_ip and
spoof_client_ip.

Also synced %ru and %>ru documentation with the current code.

This is a v4 port of master bec110e.