Thanks to everyone for their suggestions on dealing with inserts blocked by
index locking.
My eventual solution was to remove the REFERENCES constraints on the
affected tables and move referential integrity into the application - not
ideal, but faster to implement than the alternatives.
Suggested solutions were:
* Load file into temporary table, and insert into primary table from
temporary (Dennis Gearon, David Olberson)
* Convert data to insert statements and (I think) run each in a separate
transaction (Jeff Eckerman)