implement #986 - camera flash 'tweak'

Implement the suggested feature that a camera's flash actually update
hero's memory of the map as it traverses across the level.  Turned
out to be more work than anticipated despite having the code for a
thrown or kicked lit candle or lamp to build upon.

Among other things it needed to update the circle code to handle
previously unused radius 0 to operate on the center point only.  I've
never touched that before and hope this hasn't introduced any bugs.

Also removes several instances of vision code operating on column #0.
(At least one is still present.)

doc/fixes37.0

@@ -324,6 +324,8 @@ extended achievement and conduct fields for xlogfile
 record amount of gold in hero's possession in xlogfile
 new objects:  amulets of flying and guarding
 new monsters:  displacer beast ('f') and genetic engineer ('Q')
+make camera flash which reveals previously unseen map features or objects or
+	monsters record those on the hero's map; monsters revert to 'unseen'
 
 
 Platform- and/or Interface-Specific New Features