more buglist crystal ball detection

<Someone> wrote:
- If I set the 'boulder' option, shouldn't I be able to give the
  symbol I define for them at the crystal ball "object or
  monster symbol" prompt and have it work?
- Could ']' be added as a synonym for 'm', as with genocide?
- set boulder symbol to '3'; use '/' or ';' to examine a
  boulder. Result is "unknown creature causing you disquiet
  co-located with a boulder" even though there's no warning
  glyph '3' there.

doc/fixes34.3

@@ -58,6 +58,9 @@ you could specifiy '~' with crystal ball and have it try to detect monsters,
 allow a crystal ball to detect ghosts-and-shades via space key,  and display
 	the results using detected_mon_to_glyph() so that they show up in 
 	inverse video
+allow a crystal ball to detect boulders using the user-defined boulder symbol
+allow a crystal ball to detect mimics via ']'
+prevent boulder option from accepting a symbol that matches a monster symbol
 
 
 Platform- and/or Interface-Specific Fixes