We now depend on a newer GLib feature here to check the right
repositories based on the OS we are running on.
As soon as we can break API with AppStream 1.0, all of this logic can be
improved further and be generalized.

…nd origin

Resolves: #420

Use lxml to get the list of XDG categories from the DocBook file using
XPath queries; this simplifies the code a bit, and makes it more robust.

There is no change in the extracted data.

This is actually a rather steep requirement that I am not totally
comfortable with, as it complicates backports. However, we have
accumulated a really huge amount of workarounds for Meson issues, and
there are subtle bugs in older versions which do cause occasional
trouble. All of this is fixed in 0.62, so to lessen the maintenance
burden on this stuff, we just depend on that version with this release.

Resolves: #386

CC: #389

Possibly the last time I'm doing this, it's really not worth the effort.

Using the version available in Bullseye should be pretty sane by now.
Since more recent releases also have a lot of bugfixes that we want, we
may jump to an even higher version later, to avoid complicated version
checks in the build files.

msgfmt escapes all XML, even though we don't want that for MetaInfo
files description markup. Itstool does not have this issue, so let's use
that instead. This feature should probably be part of the i18n Meson
module in the future, so it is less of a hack to use.

Resolves: #357
This is a bit of a workaround, but I do not want AppStream to become an
authority on license-freeness. The DFSG/FSF/OSI are the better authority
on that. But with the DFSG override list we can at least say "if it's
free enough for Debian main, it's considered to be a free license by
AppStream too".

We don't translate this for now, until the tool has received wider
testing.

This is more consistent with other uses of multiarch tuples.

Resolves: #341

Those files were originally seen as data, not code and therefore I
assumed people would feel free to use them wherever they wanted, but
given AppStream itself it GPL/LGPL-licensed, some people needed
clarification that these files can be freely copied or merged with other
non-copyleft or non-LGPL code.
So, this commit adds a license header to clarify that they're under the
usual "do what you want but don't hold me liable" FSFAP license.

This list may be used in future to ensure more uniform platform names
for release artifacts.