ESC-228 ESC-227 Corrections for metrics counters and send-on-quit delivery.

Wanted to avoid computing metrics for duplicate requests as much as
possible, they artificially depress averages but missed an opportunity
and was including them in the counts.  The non-texture case is solid.
Textures are.... confounding still.  Do a better job of trying to send
one last packet to the grid when quitting.  It is succeeding now, at
least sometimes.  Put a comment in base llassetstorage.cpp pointing
to cut-n-paste derivation in llviewerassetstorage.cpp so that changes
can be replicated.  Hate doing this but current design forces it.