calculating shop price adjustments (trunk only)

Fix the second of a couple of minor things I noticed when viewing
that guy's ttyrec about a hidden inventory item which turned out to be
scrolls of scare monster on the used-up items section of his shop bill.

     He had a lot of scroll prices which started as $X00 and were changed
to $Y99 due to integer division roundoff when being hit with a 1/3 price
increase for unID'd items followed by 1/2 price increase for low charisma:
  100  ->  133  ->  199
  200  ->  266  ->  399
Forcing things to round up instead of truncate would help in some cases
but yield $Z01 in others.  Rather than doing that, this accumulates the
adjustment factors and then uses them to make one calculation which gives
a better result:
  100  ->  200
  200  ->  400
Other values and/or other adjustments might not work out so well, but I
don't think they'll ever become prices which look worse than before.
For a single increase of 1/3, 100 still yields 133 but 200 now gives 267
(so ends up differing from the combined price for two 100->133 items).

doc/fixes35.0

@@ -373,6 +373,7 @@ for poly'd hero hiding on ceiling, attack by sea monsters won't move them
 	into hero's position unless it is over water or they're already on land
 for poly'd hero hiding on ceiling, attack by long worm might fill hero's
 	destination with worm's tail, so double check and maybe choose again
+when shop prices are adjusted, handle roundoff (integer truncation) better
 
 
 Platform- and/or Interface-Specific Fixes