ESC-154 ESC-156 Metrics integration across threads

Using unpause() method in derived class rather than wake() in furthest base class
solved the stalling problem.  I still think too many levels of the
LLTextureFetch hierarchy are keeping thread state, however.  The
LLViewerRegion instance an agent enters doesn't necessarily have its
region_id yet, that only comes after the handshake, if any.  So add
a few more metrics insertion points to propagate region into metrics.
Finally, try to launch a final metrics report when a quit is initiated.