xo is generating thousands of Postgresql Enum golang struct

[zhany]

Hi, recently I updated the xo version and found out that xo is generating thousands of postgresql enum golang structs for one postgresql enum.

After a little investigation I figured that after PR #337 this issue appeared. The root cause might be releted to this postgresql query
in models/enum.xo.go (line 18-23):

SELECT  
c.relname AS table_name, t.typname
FROM pg_class c, pg_type t  
JOIN ONLY pg_namespace n ON n.oid = t.typnamespace  
JOIN ONLY pg_enum e ON t.oid = e.enumtypid  
WHERE n.nspname = $1

The pg_class table is added in the query without any join criteria or where criteria, thus it is generating tons of results for one enum type.