Change mkfifo to use an octal argument for MODE (bug #45054). * NEWS: Announce switch from decimal to octal MODE for mkfifo. * file-io.cc (convert): Add a FIXME note that this function is repeated in * syscalls.cc. * syscalls.cc (convert): New function to convert from one base to another. * syscalls.cc (Fmkfifo): Change docstring to note that MODE argument is now octal. Convert MODE from octal to decimal before calling octave_mkfifo(). Add BIST tests. * __gnuplot_get_var__.m, __gnuplot_ginput__.m: Change instances of MODE argument in m-files from decimal to octal.