Converted frequently occuring setting lookups to LLCachedControl

Added LLObjectList::getAvatar(LLUUID) for type-safe and quicker lookup
Added F32 overload to LLSD because using F64 needlessly is silly.
   (And its lack of F32 overload caused issues with LLCachedControl<F32>)

indra/newview/lltoolmgr.cpp

@@ -239,8 +239,9 @@ bool LLToolMgr::inBuildMode()
 	// when entering mouselook inEdit() immediately returns true before 
 	// cameraMouselook() actually starts returning true.  Also, appearance edit
 	// sets build mode to true, so let's exclude that.
+	static LLCachedControl<bool> build_btn_state("BuildBtnState",false);
 	bool b=(inEdit() 
-			&& gSavedSettings.getBOOL("BuildBtnState")
+			&& build_btn_state
 			&& !gAgent.cameraMouselook()
 			&& mCurrentToolset != gFaceEditToolset);