In case anyone in the world is interested other than me, a useful
empirical discovery when exporting from 9.X to an earlier 8.4 based
server is to set the bytea_output variable at the level of the
ALTER DATABASE bloodbank SET bytea_output='escape';
Then the bytea data will come out old style and 8.4 is happy. You
could also set this variable in pgadmin. Note this only affects sql
based (plain) dumps, not the binary compressed format.
Afterward you could set it back from 'escape' to 'hex' if you like.