dj.Relvar/importAll should throw error or warning on duplicate insert

[jakereimer]

importAll currently inserts backed-up tuples using inserti, which discards errors. As a result, a user cannot be sure that their call to importAll actually inserted the data without manually checking that there are no duplicates already in the table. The insert should be performed via standard insert (preferred) or at the very least a warning should be issued if the import was not completed successfully.

[ixcat]

discussion: need to xcheck inserti w/r/t suppress_errors in python, adjust/revisit importAll