[JENKINS-12307] More helpful error message for getItemTypeDescriptorOrDie on a non-collection field.

[FIXED JENKINS-15292] Revert "setting maven home is enough for global settings to be m.getHome()/conf/settings.xml"

This reverts commit 51d5220f.

hudson.maven.MavenUtil#createEmbedder set GlobalSettingsFile to MavenHome/conf/settings.xml by default so I can't explain this regression

... based on Jesse's feedback to 1f83338d

/computer/*/doDelete should try harder to remove even a “zombie” Computer with no associated Node.

Conflicts:
	changelog.html
	core/src/main/java/jenkins/model/lazy/SortedList.java

If unwrap returns null, we need to fall through to load to try it again.
(cherry picked from commit 04c87d8d)

If a build record gets GCed, a load is attempted, and that fails, then RunMap can return null. Not sure if this alone would explain the entirety of JENKINS-15465, but this is a related fix.
(cherry picked from commit ca44a90e)

I can't really think of how null ends up in the resulting list, but adding a check in Iterator to detect that situation.

Also, improved the efficiency of the subList implementation.
(cherry picked from commit 807dc717)

If unwrap returns null, we need to fall through to load to try it again.

If a build record gets GCed, a load is attempted, and that fails, then RunMap can return null. Not sure if this alone would explain the entirety of JENKINS-15465, but this is a related fix.

Ensure that SortedList clones the underlying data list.
Without this changes to a clone also change the original list.
(cherry picked from commit 761c4379)

Ensure that SortedList clones the underlying data list.
Without this changes to a clone also change the original list.

adding more probe.

since these tags are used in sidepanel, don't make assumption that "it" object is rendering the current URL.

I can't really think of how null ends up in the resulting list, but adding a check in Iterator to detect that situation.

Also, improved the efficiency of the subList implementation.