Bug#879044: gobject-introspection: mini-policy: clarify where language overrides should be shipped

[Changwoo Ryu]

But one problem of having Python (for example) overrides file in
gir1.2-* package is, that it creates unnecessary dependency on python
even for non-python rdepends.

Currently some gir1.2-* packages with Python overrides files have
intentionally missing python dependency to avoid such unnecessary
dependency and have lintian-overrides to avoid lintian error
python-package-missing-depends-on-python.
(https://lintian.debian.org/tags/python-package-missing-depends-on-python.html)

I'm not against having language overrides in gir1.2-* packages. But
when we choose to do it, it would be great if the mini policy clarify
this: If gir1.2-foo has Python overridess file, should gir1.2-foo
depend on Python? If not, is it OK to have lintian-overrides?