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.)

include/vision.h

@@ -52,7 +52,7 @@
 /*
  *  Circle information
  */
-#define MAX_RADIUS 15 /* this is in points from the source */
+#define MAX_RADIUS 16 /* this is in points from the source */
 
 /* Use this macro to get a list of distances of the edges (see vision.c). */
 #define circle_ptr(z) (&circle_data[(int) circle_start[z]])