Merge branch '2888_cleanup'

Merge branch '2888_cleanup'

* 2888_cleanup:
  Fix of DOXYGEN docs: @return instead of @returns
  src/filemanager/command.c: add DOXYGEN doc little little code cleanup.
  (enter): use GString instead of hand-made memory (re)allocation.
  Clarify of sig_atomic_t usage (got from Mutt).
  Define winch_flag as volatile sig_atomic_t.
  Fixups of SIGWINCH handling.
  Don't exit after migration of configuration files.
  Tweak sources for --with-x/--without-x option.
  Init file highlighting only in full mode.
  (exit_subshell): return gboolean instead of int.
  lib/strutil/strverscmp.c: add missing include of config.h.
  (fish_linear_abort): type accuracy.
  (fish_file_store): remove unnecessary 'was_error' variable.
  (fish_file_store): type accuracy to avoid counter overflow while copiyng huge files.
  (ftpfs_file_store): type accuracy and simplify conditions.
  Ticket #2888: code cleanup before 4.8.7 release.