xgettext: Support per-file options
* autogen.sh (GNULIB_MODULES_TOOLS_FOR_SRC): Add getsubopt.
* gettext-tools/src/xgettext.c: Include <fnmatch.h>.
(long_options): Add --options.
(main): Handle --options. Factor out language guessing to...
(filename_to_language): ...here.
(usage): Mention --options.
(enum suboption_type): New enum.
(suboption_tokens): New variable.
(struct suboption_ty, struct suboption_list_ty,
struct suboption_list_list_ty): New struct.
(suboption_list_destroy, suboption_list_insert,
suboption_list_list_destroy, suboption_list_list_insert): New function.
(suboptions): New variable.
