The error messages from gnulib need to be included into nano's POT file
so that those messages get translated when nano is built on a platform
where the modules that contain the messages get used.
This fixes https://savannah.gnu.org/bugs/?56107.
Bug existed since gnulib support was added in version 2.8.0.
The relevant modules were added by commits 3deec435 and 272345cc.
5459f56f6d