examples: Upgrade to newest Makevars.

examples: Upgrade to newest Makevars.

* gettext-tools/examples/hello-*/po/Makevars (PACKAGE_GNU, MSGINIT_OPTIONS,
PO_DEPENDS_ON_POT, DIST_DEPENDS_ON_UPDATE_PO): New variables.
* gettext-tools/examples/hello-*/configure.* (AM_GNU_GETTEXT_VERSION): Require
version 0.19.8.
* gettext-tools/examples/po/xsmallpot.sh (hello-c++-kde): Likewise.
* gettext-tools/examples/hello-*/m4/Makefile.am (EXTRA_DIST): Update list of .m4
files.
* gettext-tools/examples/hello-*/autoclean.sh: Likewise.
* gettext-tools/examples/check-examples (func_check_maintainerclean,
func_check_maintainerclean_vpath): Allow left-over .po~ files.