[QGIS-Developer] 3.4 backports

[Nyall Dawson]

Hi all,

Just a quick plea that during this freeze period please think
carefully about the suitability of backporting fixes to 3.4. At this
stage in its lifecycle 3.4 should only receive absolutely mission
critical fixes (such as crash fixes or data corruption issues).

The consequence of regressions in 3.4 caused by backporting minor bug
fixes much outweighs the benefits of fixing these bugs. While the
backport label makes 3.4 backports easy to do, it does not guarantee
their safety or suitability.

Thanks!
Nyall