Add an HTTP policy class for inventory operations using four (4)

connections.  Convert background and foreground fetches, both
items and folders/inventory and library, to use new HTTP.
Non-fetch inventory operations continue to use LLHTTPClient
(at least for now).  Error handling and retry on fetches wasn't
100% previously and that's still the case.  I'll rip through
this again to clean that up.  Cleaned up logging in much of
the inventory code with consistent labels on logging events
and correct macros (removed deprecation warnings).

This started as an attempt to get libcurl to do pipelining
on POSTs and PUTs.  Discovered that this is going to be
very difficult to support in general in libcurl.  May
look at that again in the future.