We were using GIMP_UNSTABLE extensively to differentiate development
from stable code. But there is actually another level of development
code. Basically GIMP_UNSTABLE tells you are on the development branch,
e.g. for current branches, that you are on 2.99.* versions (vs. 2.10).
This depends on the minor version oddness.
GIMP_RELEASE will tell you if it's a release or a in-between-releases
code. This works with the micro version which must be even on release.
Any odd number means you are basically using random git code.
There can be any combination of GIMP_RELEASE and GIMP_UNSTABLE. For
instance 2.99.12 is a release of the unstable branch, whereas 2.10.33 is
development code of the stable branch.
I use this first in the update code as we were using GIMP_UNSTABLE for
both concepts but it made it harder to test. Now:
* GIMP_DEV_VERSIONS_JSON environment variable is only available on
development code, not on release (whether stable or unstable).
* The weekly check limitation is also only for releases (dev code just
check at every startup to quickly detect issues and regressions).
* Whether to look on testing website or public website json file depends
on the code being a release or not.
* Finally only whether to check "DEVELOPMENT" or "STABLE" sections in
the json file depends on whether we are on stable or unstable
branches.
(cherry picked from commit fbb5b40345)
e4a9f1b35a