use gnulib to print --help and --version

* Makefile.am: update help2man invocation and add MAINTAINERCLEANFILES
* bootstrap.conf: include dirname, propername, and version-etc-fsf modules
* configure.ac: remove COPYRIGHT_YEAR from config.h
* doc/hello.texi: remove short options -h and -v
* po/POTFILES.in: add lib/version-etc.c to translations
* src/hello.c: remove print_version(), and rename print_help() to usage()
* src/system.h: add inline functions to print version and usage info
use standard error printing facilities

* bootstrap.conf: add error module
* src/hello.c: use error() where needed
demonstrate how to add information to a manual page

* man/hello.x: ditto
update gnulib

* gnulib: jump 293 commits a head
update NLS file sources

* .gitignore: ignore 'make po-check' files
* Makefile.am: ignore gnulib/ directory contents when po-check'ing
* po/POTFILES.in: add file po-check found not to be part of translations