cref_analyze_ gives superfluous errors for non-object segments

[Eric Swenson]

If you attempt to produce a crossref, you get lots of spurious errors from cref_analyze_ for every non-object segment it encounters (e.g. exec_coms, data files, etc.). The error messages look like:

cref_analyze_: There is an internal inconsistency in the segment. volume_sys_vols.dump is non-object.

These should probably just be surpressed, as these are not really errors and muddy up the output so that real errors are obscured.