add get_directories

dtool/src/prc/configVariableSearchPath.h

@@ -71,6 +71,7 @@ PUBLISHED:
   INLINE bool is_empty() const;
   INLINE int get_num_directories() const;
   INLINE const Filename &get_directory(int n) const;
+  MAKE_SEQ(get_directories, get_num_directories, get_directory);
 
   INLINE Filename find_file(const Filename &filename) const;
   INLINE int find_all_files(const Filename &filename,