[JENKINS-16845] Refinement to hotfix: if build field has already been cleared due to earlier warning, do not throw a new NPE.

This bug indicates that people are having trouble understanding who's
responsible for aborting the build. This change records that
information through the logger.

A recent Stapler update caused the Jelly facet to ignore *.xml.
So need to use raw j:include (as plugins were doing), not st:include (as core did).

Most notable, cvs 1.6 → 2.8, to get the critical fix of removing the mail address resolver.

(cherry picked from commit 9858bf1e)

This is deemed important because we ship Jenkins without security setting by default.