SH-2243 work in progress -- don't use gl_FragColor or gl_FragData for outputs -- no more deprecation warnings on nvidia

STORM-1562 Potential fix for crash in LLCurl::run -- make sure all ref counted members of llsecapi are thread safe

STORM-1562 Potential fix for crash in LLCurl::run -- don't run curl_multi_perform from multiple threads simultaneously.

Now that we have unit tests that require assertion failure if you try to
delete an LLInstanceTracker subclass instance with an iterator loose, having
llassert() "sometimes" compile away (whimsically, depending on platform as
well as build type!) makes those tests fail. Use llassert_always() instead.

The recent class-static LLInstanceTracker::instance_iter and key_iter
reference count is intended to guard against deleting an instance of an
LLInstanceTracker subclass during iteration. Add tests for that functionality.

Generalize the notion of getting some chunk of "static" storage: introduce
LLInstanceTrackerBase::getStatic() template method. Define StaticData struct
containing the InstanceMap (or InstanceSet, for that specialization) along
with the S32 that caused the VS2010 linker so much grief. Completely eliminate
that S32 as an actual class-static member, qualifying all references with the
struct returned by getStatic().
In LLInstanceTrackerBase::getInstances(), use one std::map lookup instead of
three.

Renamed LLCurl::check_curl_code() and LLCurl::check_curl_multi_code() to prevent ambiguous name build error.

 * Removed check_curl_code and check_curl_multi_code from the global namespace.
 * Added comments documenting which thread the public methods of LLProxy should be called from.
 * Corrected grammar in LLSingleton.h
 * Fixed a buffer scope problem in llpacketring.cpp.