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.

include/rm.h

@@ -266,7 +266,9 @@ struct symparse {
 /* misc symbol definitions */
 #define SYM_BOULDER 0
 #define SYM_INVISIBLE 1
-#define MAXOTHER 2
+#define SYM_PET_OVERRIDE 2
+#define SYM_PLAYER_OVERRIDE 3
+#define MAXOTHER 4
 
 /* linked list of symsets and their characteristics */
 struct symsetentry {
@@ -306,8 +308,10 @@ extern const struct symdef defsyms[MAXPCHARS]; /* defaults */
 extern const struct symdef def_warnsyms[WARNCOUNT];
 extern int currentgraphics; /* from drawing.c */
 extern nhsym showsyms[];
-extern nhsym l_syms[];
-extern nhsym r_syms[];
+extern nhsym primary_syms[];
+extern nhsym rogue_syms[];
+extern nhsym ov_primary_syms[];
+extern nhsym ov_rogue_syms[];
 
 extern struct symsetentry symset[NUM_GRAPHICS]; /* from drawing.c */
 #define SYMHANDLING(ht) (symset[currentgraphics].handling == (ht))