Try putting an initial slash in that path string, to make it absolute:

$dsn .= ";mysql_read_default_file=/home/gmacfadd/public_html/cgi-bin/d
+ubois/.my.cnf";
[download]

(update: and if that doesn't work, be sure to check permissions along every step of that path; it needs to be readable by both the web server and the mysql daemon (which typically runs with username "mysql"), so rwxr-xr-x on each directory in the path, and rw-r--r-- on the config file itself.)