Zero byte sized files in source tarballs

[Robbin Kulicki <rkulicki gmail com>]

Why do some GNOME source distribution packages such as Banshee, Cheese,
Evolution, and NetworkManager contain the following 0 byte sized files:
intltool-extract.in
intltool-merge.in
intltool-update.in

What are these files used for?

Other packages that rely on intltool such as Epiphany, gcalctool, and
Rhythmbox do not include those files.

Thanks,
Robbin Kulicki