Allow a hero polymorphed into a giant to move to a boulder's spot
via m<dir> no-pickup move, instead of having to push it until the
way is blocked by something and then having push failure move hero
to the spot.
Also change m<dir> when not a giant to no longer push the boulder.
No time will elapse when not moving unless hero who didn't know
that there was a boulder there learns that one is. Since no actual
push attempt gets performed, player doesn't learn whether there is
anything beyond the boulder that inhibits it from being pushed.
fc00ced6f4