Merge pull request #764 from akohlmey/improved-variable-error-reporting

  void remove(int);

  void grow();

  void copy(int, char **, char **);

  double evaluate(char *, Tree **);

  double evaluate(char *, Tree **, int ivar=-1);

  double collapse_tree(Tree *);

  double eval_tree(Tree *, int);

  int size_tree_vector(Tree *);

  int compare_tree_vector(int, int);

  void free_tree(Tree *);

  int find_matching_paren(char *, int, char *&);

  int find_matching_paren(char *, int, char *&, int ivar=-1);

  int math_function(char *, char *, Tree **, Tree **, int &, double *, int &);

  int group_function(char *, char *, Tree **, Tree **, int &, double *, int &);

  int region_function(char *);

  double constant(char *);

  int parse_args(char *, char **);

  char *find_next_comma(char *);

  void print_var_error(const char *, int, const char *, int);

  void print_tree(Tree *, int);

};