Errors on contact import are often silently ignored

When importing contacts in /CRM/Import/Parser/Contact.php there is a verification step and an import step.

On the import step, a number of errors are silently ignored. Particularly this includes errors involving custom data but perhaps others as well.

This makes it quite difficult to troubleshoot problems with importing data and I think this is the root cause of many of the posts to the forums over the years about mysterious and unsolvable problems importing data.

In particular I know these two errors are not handled in /CRM/Import/Parser/Contact.php:

1. Around line 1660: $error = _civicrm_api3_deprecated_contact_check_params($formatted, $dupeCheck, TRUE, FALSE, $dedupeRuleGroupID);

2. Around line 1670: $error = _civicrm_api3_deprecated_validate_formatted_contact($formatted);

If the second line returns an error message then the import of that entire record is aborted at that point with no error message given. I assume the same happens if the first line returns and error message but I haven't tested that.

My impression is there are other errors similarly not handled in /CRM/Import/Parser/Contact.php but I could be wrong about that.

This is related to the following bugs but the lack of error reporting in the import step strikes me as a separate issue and if it is happening in more places than the two listed above, perhaps a larger issue and more work to fix:

http://issues.civicrm.org/jira/browse/CRM-10834
http://issues.civicrm.org/jira/browse/CRM-10832