MAINT-5271: Converted internal pointers to internal operation to managed shared pointers. Removed direct cast and dereference of handles.

Add to-do list to _httpinternal.h to guide anyone who
wants to pitch in and help.

sort things out or use policy classes (eventually) to arrange low
and high priority traffic.  Subjectively, I think this works better
in practice (as I haven't implemented a dynamic priority setter yet).

surprised me.  Added a retry queue similar to ready queue to the
policy object which is sorted by retry time.  Currently do five
retries (after the initial try) delayed by .25, .5, 1, 2 and 5
seconds.  Removed the retry logic from the lltexturefetch module.
Upped the waiting time in the unit test for the retries.  People
won't like this but tough, need tests.

Identified and reacted to the priority inversion problem we
have in texturefetch.  Includes the introduction of a priority_queue
for the requests that are ready.  Start some parameterization in
anticipation of having policy_class everywhere.  Removed _assert.h
which isn't really needed in indra codebase.  Implemented async
setPriority request (which I hope I can get rid of eventually along
with all priorities in this library).  Converted to using unsigned
int for priority rather than float.  Implemented POST and did
groundwork for PUT.