poly'd hero hiding feedback

When hiding as a monster, say so during the #monster command and
also list being hidden in the status section of enlightenment/^X.

     Also, prevent hiding on the floor or ceiling on the planes of air
and water.  (Didn't apply to monsters, who only hide on ROOM spots.)

     Half the change to dohide() is just revised indentation.

include/extern.h

@@ -197,6 +197,7 @@ E int NDECL(doextlist);
 E int NDECL(extcmd_via_menu);
 E int NDECL(enter_explore_mode);
 E void FDECL(enlightenment, (int,int));
+E void FDECL(youhiding, (BOOLEAN_P,int));
 E void FDECL(show_conduct, (int));
 E int FDECL(xytod, (SCHAR_P,SCHAR_P));
 E void FDECL(dtoxy, (coord *,int));