Declare some function arguments as const.

Some functions, mostly in fight.c, declared variables as pointers to
const char but passed them to functions that took pointers to ordinary
char.  The strings did not actually get modified, so adding 'const' to
the function definitions removed the warnings.

rogue4/rogue.h

@@ -619,7 +619,7 @@ void    unconfuse(void);
 char   *unctrol(char ch);
 void    unlock_sc(void);
 void    unsee(void);
-char   *vowelstr(char *str);
+char   *vowelstr(const char *str);
 char   *xcrypt(const char *key, const char *setting);
 void    w_wait_for(WINDOW *win, char ch);
 void    wait_for(char ch);