I was testing 1.4.0 in a database here before it was it was 1.4.0. When I went to upgrade that database to 1.4.1, I got

ERROR:  function "spoly" already exists with same argument types

My solution was to change all the "CREATE FUNCTION" statements in the upgrade script to "CREATE OR REPLACE FUNCTION". The upgrade then worked fine. I feel this should be the standard practice for all upgrade scripts, past and future.