Be more verbose about the Queue, Class, or what-have you that failed to load

This is relevant when the format contains a custom field which applies
to only some of the results.
If the custom field failed to load, prevent an undef warning once per row

A warning has already been printed; no need hide it under a spew of "Use
of uninitialized value in concatenation" messages.
Increase log level for CF load failure in ColumnMap

This makes the failure slightly more evident, now that the per-row
warnings are suppressed.
Merge branch '4.2/columnmap-cf-warnings'