add handling of configuration file in the Windows shared system
directory. (Bug #5354)


extra/my_print_defaults.c:
  Print out list of default files that will be used.
include/my_sys.h:
  Add new my_print_default_files() function.
mysys/default.c:
  Increase MAX_DEFAULT_DIRS to handle shared Windows directory,
  move the logic for handling the Windows (and OS/2) system directories
  into init_default_directories(), and generalize handling of
  configuration file extensions.