Avoid using GL_ARB_timer_query functionality when not supported and protect against probably-not-NULL current bound shader pointer

Incorporate the new libcurl 7.38.0 build with curl bug 1420
workaround.  Add developer-centric testing code to evaluate
the workaround or a future fix for 1420.

The HttpRequest objects used in inventory ops are created lazily
when needed.  The update() operation didn't protect against their
not being created.  Added some guard tests around the update()
operations and we're good.

FIX INTL-151 re-committed translation for Viewer Set41; this brings back missing translation after the last merge

on the HTTP requests for inventory.  We'll benchmark with that
and see how it goes.  Document some of the history of the
background fetcher for future devs.  Suggest some future
projects to make things faster.  Pointers on using LLSD with
the llcorehttp library in the readme.  And restructured
the LLSD onCompleted() processing phases using do{}while(false)
which produced a code flow that is fairly attractive.

accept headers in mesh and textures.  For texture metrics
reporting, use the AP_INVENTORY policy class which is
non-pipelined and pointing (usually) in the right direction.
Use a do-while(false) structure to manage common exit path
code in onCompleted() methods.  Identical to a 'goto' but
might amuse the pedantic.  Tuning on background fetch to
have it cycle faster.  This is experimental.  I suspect
with HTTP balancing in llcorehttp, we can do away with the
timers here.

of used handles and a fast handle factory that's thread-
correct.

reproduce data corruption via timeouts.