announce-gen: minor issues

[Akim Demaille]

The two attached patches provide minor improvements to
announce-gen.  The first one was prompted by the fact
that I had an error message whose origin was unclear.

* build-aux/announce-gen: When parsing command line options,
prefer "announce-gen: option --release-type requires an argument"
to "Option release-type requires an argument".

The second one addresses a portability issue.

* build-aux/announce-gen (sizes): Invoke du with -h
instead of --human.

0001-announce-gen-Improve-diagnostics.patch
Description: Binary data

0002-announce-gen-portability.patch
Description: Binary data