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.

code to use utils for any LLSD interfaces.

the TC builds failing on these tests.  Appears to be a
conflict/race condition on a temporary file.  Changed the
name of the file.  Should use a tempname()-like API but
this will do for a unit test.

as transfers can appear delayed with deep pipelining and more
requests in the pool.  Added bad HTTP status error (typically
getting a 0 back as HTTP status from libcurl) to the list of
retryable errors.  There's a response stream problem with libcurl
and pipelining that induces this problem.  Retrying helps but
may not be entirely safe.  Watch bug 1420 on the libcurl sourceforge
bug tracker.  Extend options of test/example program to include
un-ranged requests.  Document the excessive data transfer induced
when ranged requests are disabled.  This is an abnormal mode for
very rare users so we'll just eat that for now.

Reverted previous two fixes and modified LLTextBase::changeLine()