Combine GRIB2 GDT 90 with bitmap data.
Clarify public status of iris.tests
Merge pull request #1469 from rhattersley/deprecation-tweak

Clarify status of iris.tests
Merge pull request #1468 from rhattersley/grib-integration

Combine GRIB2 GDT 90 with bitmap data.
Support for grib gdt5 saving.
Review changes.
Fix grib comparison results -- for newer gribapi only.
Support for grib gdt5 saving.
Fix grib gdt5 load and add roundtrip test.