update to gengetopt-2.17

gengetopt-2.17 has an improved help management, thanks again to Lorenzo
Bettini for implementing my suggestions. The help texts of the options
are contained in an array which is defined in xyz.cmdline.c and declared
as extern in xyz.cmdline.h.

In order to link more than one xyz.cmdline.o into a single binary,
these arrays must have different names. So use the --arg-struct-name
option of gengetopt for each receiver/filter.