some symbol tweaks

A few symbol-related modifications:

- fulfill a request from a blind player to allow them to
  specify a unique/recognizable character for all pets and/or
  the player in the config file for use when using a screen
  reader (S_player_override, S_pet_override). Requires sysconf
  setting ACCESSIBILITY to be set to have an effect, although
  they can still be specified in the config file.

- Config file SYMBOLS entries were not working properly on
  the rogue level. Allow ROGUESYMBOLS as well as SYMBOLS to be
  specified in the config file independently.

- When values are moved into showsyms[], the overriding SYMBOLS
  or ROGUESYMBOLS entry from the config file is used if there is
  one; if there is no overriding value for a particular symbol,
  the loaded symset value is used; if there is no symset entry
  loaded for the symbol then a default symbol is used.

doc/Guidebook.mn

@@ -24,7 +24,7 @@
 .ds vr "NetHack 3.6
 .ds f0 "\*(vr
 .ds f1
-.ds f2 "October 1, 2019
+.ds f2 "October 27, 2019
 .
 .\" A note on some special characters:
 .\" \(lq = left double quote
@@ -2731,7 +2731,7 @@ See the \(lqConfiguring Message Types\(rq section.
 .lp MENUCOLOR
 Highlight menu lines with different colors.
 See the \(lqConfiguring Menu Colors\(rq section.
-.lp SYMBOLS
+.lp SYMBOLS, ROGUESYMBOLS
 Override one or more symbols in the symbols files.
 See the \(lqModifying NetHack Symbols\(rq section.
 .pg
@@ -4375,8 +4375,8 @@ Set the name of the symbol set that you want to load.
 Set the name of the symbol set that you want to load for display
 on the rogue level.
 .pg
-You can also override one or more symbols using the SYMBOLS config
-file option. Symbols are specified as name:value pairs.
+You can also override one or more symbols using the SYMBOLS and
+ROGUESYMBOLS config file options. Symbols are specified as name:value pairs.
 Note that
 NetHack escape-processes the value string in conventional C fashion.
 This means that \\ is a prefix to take the following character literally.
@@ -4570,6 +4570,8 @@ X	S_xorn	(xorn)
 Y	S_yeti	(apelike creature)
 Z	S_zombie	(zombie)
 z	S_zruty	(zruty)
+ 	S_pet_override	(pet override if sysconf accessibility is set)
+ 	S_player_override	(player override if sysconf accessibility is set)
 .\"TABLE_END  Do not delete this line.
 .TE
 .pg
@@ -4612,7 +4614,12 @@ configuration file will cause the game to run in a manner accessible
 to the blind.
 After you have gained some experience with the game
 and with editing files, you may want to alter settings via \fBSYMBOLS=\fP
+and \fBROGUESYMBOLS=\fP
 in your configuration file to better suit your preferences.
+See the previous section for the special symbols S_pet_override 
+to force a consistent symbol for all pets and and 
+S_player_override to force a unique symbol for the player character
+if \fBaccessibility\fP is enabled in the sysconf file.
 The most crucial settings to make the game accessible are:
 .pg
 .lp symset:NHAccess