First HTTP pipelining viewer. Enable pipelining for

GetTexture and GetMesh2 at a pipeline depth of 5.  Create
global debug option, HttpPipelining, to enable and disable
HTTP pipelining (defaults to true).  Tweak texture and
mesh low- and high-water request levels based on pipelining
status and depth.  Fixup texture console which was damaged
in a recent release.  Split logging of the no-request
HTTP error case into two cases:  one for missing URL in
HTTP request, one for HTTP request not created.  A refactor
in llcorehttp is coming:  I will be moving all libcurl-
using code into libcurl-specific modules.