[FIXED JENKINS-26601] Partly reverting #1453 to avoid hitting https://github.com/google/guice/issues/899.

(cherry picked from commit 00c858d4 into 1.599 rc)

In this environment, Util.createSymlink and .isSymlink are implemented, but resolveSymlink is not.
(cherry picked from commit 388c4b5e)

Conflicts:
	changelog.html

(cherry picked from commit 75c8c31f)

(cherry picked from commit 0633beef)

[FIXED JENKINS-25234] Improve readability of the 'schedule build' tooltip

SCM._for is actually @CheckForNull.

[FIXED JENKINS-20606] Wrong spelling in Russian localization

Updating SingleFileSCM to nondeprecated overload of checkout.

This allows @Initializer to have parameter injection

This demonstrated that we actually need to call EnvVars.overrideAll explicitly (as CoreWrapperStep already did).