GDAL 2.3.1

[Sebastiaan Couwenberg <sebastic@xs4all.nl>]

GDAL 2.3.1 has been released and is available in unstable. Not
transition was required, the virtual ABI dependency was kept at gdal-2-3-0.

Because the gdal build triggered autopkgtests for r-cran-mi which failed
due to r-base-core also being updated, testing migration is penalized by
10 days, so it will take 15 days instead of 5 (or even 2) for the gdal
package to migrate to testing.

The autopkgtest infrastructure is nice, but its current implementation
is somewhat lacking. Its inability to only update a single package to
pinpoint the actual package that caused test regressions being the most
annoying.

Kind Regards,

Bas