Variable Size Regions! Support for prehash RegionSizeX and large patches. (WIP)

Mostly from Ukando, tweaked a bit to be cleaner, and a little less dramatic.

decode_patch_header now takes a bool optionally, as third argument.
_PREHASH_RegionSizeX is the only used of the two _PREHASH_RegionSize*.
llsurface.cpp: Copy the connectNeighbor for variable size regions almost directly from Ukando
llsurfacepatch.cpp: Patch code from ukando and voodoo.
Changed hardcoded 256 constants and such to width functions in: llglsandbox.cpp, llsurface.cpp, llviewerregion.cpp, llviewerparcelmanager, llviewerparcelmgr.cpp, llvowater.cpp, llworld.cpp
Use region specific width in: llagent.cpp, llglsandbox.cpp, llmanip.cpp, llmanipscale.cpp, llpanelobject.cpp, llviewerbject.cpp, llwind.cpp
Use 256 in llnetmap.cpp in places...
llfloaterregioninfo.cpp: Aurora grid has wacky textures.
Add LLViewerParcelMgr::widthUpdate() for updating mParcelsPerEdge given a region's width. Used in llstartup now.
Add LLWorld::setWidth() for getting a region's size from LLMessageSystem pointers and setting mWidth and mWidthInMeters, accordingly. Called in llviewermessage.cpp as well.

indra/newview/llmanipscale.cpp

@@ -1356,7 +1356,7 @@ void LLManipScale::renderGuidelinesPart( const LLBBox& bbox )
 
 	guideline_end -= guideline_start;
 	guideline_end.normVec();
-	guideline_end *= LLWorld::getInstance()->getRegionWidthInMeters();
+	guideline_end *= gAgent.getRegion()->getWidth();
 	guideline_end += guideline_start;
 
 	{