Three related bug fixed, two reported in U409.
+ If you zapped a wand of cold downward while hiding underwater, the uundetected
flag was not reset (but the monster case was code correctly), resulting in
an impossible error on the next attack
+ If you finished eating something you were hiding under and were attacked,
another impossible would occur
+ While checking the eating gold case, I noticed that several cases would lose
gold on the floor if the attempt to eat it failed
The first case is fixed by resetting the flag just like the monster case.
The other cases are fixed by adding code to useupf to deal with this.
eatspecial and floorfood were modified to allow useupf to be called, and
fix the 3rd bug in the process.
b53cdee210