Until now, LLEventAPI has only been able to register functions specifically
accepting(const LLSD&). Typically you add a wrapper method to your LLEventAPI
subclass, register that, have it extract desired params from the incoming LLSD
and then call the actual function of interest.
With help from Alain, added new LLEventAPI::add() methods capable of
registering functions/methods with arbitrary parameter signatures. The code
uses boost::fusion magic to implicitly match incoming LLSD arguments to the
function's formal parameter list, bypassing the need for an explicit helper
method.
New add() methods caused an ambiguity with a previous convenience overload.
Removed that overload and fixed the one existing usage.
Replaced LLEventDispatcher::get() with try_call() -- it's no longer easy to
return a Callable for caller to call directly. But the one known use of that
feature simply used it to avoid fatal LL_ERRS on unknown function-name string,
hence the try_call() approach actually addresses that case more directly.
Added indra/common/lleventdispatcher_test.cpp to exercise new functionality.

LLSDArray is a helper to construct an LLSD::Array value inline.
LLSDMap is a helper to construct an LLSD::Map value inline.
LLSDParam is a customization point, a way for generic code to support
unforseen parameter types as conversion targets for LLSD values.

Reviewed by CG.

Stored filter sub-string comparison with new string failed because of non-matching register of compared strings. Transforming the new search term to uppercase before comparing it with previous one allows to determine if filter became more or less restrictive and not to restart the search over.
Used patch provided by Satomi Ahn.

fix for SH-445: debug settings -> "CacheNumberOfRegionsForObjects" does not limit the number of object cache files

Merge viewer-development-shining up to REV 3bf724ecb7c6 (fix for SH-829: Viewer attempting to load precached images in file types that are not being used.)