Currently the DelegateSCM enforces that there is an active parent build, so that it can obtain the appropriate changeset at which to run the child job.

However, there are times where triggering the inner job is preferable, or even accidental (we don't hide all the run buttons).

We should consider allowing this direct invocation to simply construct a changeset agnostic version of the parent's SCM for its build, assuming the user has opted out of some global configuration relaxing the strict nesting requirement.