Using 'mesonbuild' as the module can cause it to use the
system-installed module and can also break if we rename the directory,
so avoid that by always using relative imports.
For each project this creates a <project>-update-po target.
When ran this updates the pot file and then merges it back
into the po files in the source directory with `msgmerge`
for project maintainers and translators.
Fixes#819
In autotools POTFILES is generated at configure time from POTFILES.in,
but Meson only looks for a po/POTFILES in the source directory, which
is awkward when trying to maintain both build systems in parallel.
Instead just use POTFILES.in as fallback if it exists but POTFILES
does not. Also print an error if neither exists.
Fixes#818
Nirbheek Chauhan
Patrick Griffis
Jussi Pakkanen
Tim-Philipp Müller
Nirbheek Chauhan