Returns whether the player is currently outdoors. "Outdoors" as defined by this function corresponds to the ability to use a mount in that specific location, not necessarily whether there is a roof above the player character's head. For example, returns 1 in Ironforge, Undercity, and the Caverns of Time, but nil in the nominally outdoor areas of instances such as Stratholme, Drak'tharon Keep, and Hellfire Ramparts. (Note that even in "outdoor" areas, standing on top of certain objects may interfere with the player's ability to mount up.)