llcorehttp implements a nice trace facility but it hasn't been attached to
an external control to date. This hands over control to a *non-persistent*
setting that can be used for QA or field diagnostics.
Isolate llcorehttp initialization into a utility class (LLAppCoreHttp)
that provides glue between app and library (sets up policies, handles
notifications). Introduce 'TextureFetchConcurrency' debug setting to
provide some field control when absolutely necessary.
Graham Madarasz