Encapsulate LFIDBearer::sActive, set with member setActive

This function caches the current type when active,
in the future it could be more useful than that.

sActive is now const, getActive returns const,
IDBearers display information, the interface should only be used for that

indra/newview/llnameeditor.cpp

@@ -86,7 +86,7 @@ BOOL LLNameEditor::handleRightMouseDown(S32 x, S32 y, MASK mask)
 		new_menu = mIsGroup ? "menu_nameeditor_group.xml" : "menu_nameeditor_avatar.xml";
 	}
 	if (!new_menu.empty()) setContextMenu(LLUICtrlFactory::instance().buildMenu(new_menu, LLMenuGL::sMenuContainer));
-	sActive = this;
+	setActive();
 
 	return LLLineEditor::handleRightMouseDown(x, y, mask);
 }