Merge branch '3915_cleanup'

Merge branch '3915_cleanup'

* 3915_cleanup: (25 commits)
  Update po/*.po files.
  (init_subshell): use openpty() to open master/slave devices for subshell.
  m4.include: move Gnulib modules to their own subdirectory.
  (vfs_preallocate): check mc_global.vfs.preallocate_space before call.
  (filegui__check_attrs_on_fs): check copymove_persistent_attr before call.
  (dlg_run_done): fix possible NULL dereference.
  (dlg_init): fix possible NULL dereference.
  doc: clarify description of system-wide confiduration files.
  Clarify usage of FL_NONE value.
  extfs: optimization: get rid of extra memory duplication.
  (file_mask_dialog): don't return an empty string.
  (file_mask_dialog): grammar.
  (str_ptr_array_join): constify argument.
  (extfs_get_path): use standard VFS flags.
  (extfs_find_entry): use standard VFS flags.
  extfs: constify some function arguments.
  extfs: refactoring: rename structures...
  extfs: refactoring: rename some structure members...
  extfs: refactoring: struct inode: use struct stat instead of separate members.
  extfs: refactoring: use GSList to store archive list.
  ...