Allow the builtin function mkdir to create missing parent directories * bootstrap.conf : Add the mkdir-p and savewd gnulib modules. * file-ops.cc (static int make_ancestor (const char*, const char*, void*)): New function. (int octave_mkdir (const std::string&, mode_t, std::string&, bool): Add fourth argument and use it to conditionally select whether to make the missing parent directories. * file-ops.h (int octave_mkdir (const std::string&, mode_t, std::string&, bool): Add fourth argument. * lo-cutils.c (struct mkdir_options): New structure (static void announce_mkdir (const char*, void*), static int process_dir (char *, struct savewd *, void *), int octave_mkdir_parents (const char *, mode_t, int (*make_ancestor) (const char *, const char *, void *)): New functions. * lo-cutils.h (int octave_mkdir_parents (const char *, mode_t, int (*make_ancestor) (const char *, const char *, void *)): New function. * dirfns.cc (Fmkdir): Call octave_mkdir with the make_parents argument set to true.