Add a warning.

Author: n-g

library/oss/postgres/prepare/database/functions.sql

@@ -8,6 +8,7 @@
 -- The functions below provide ensure semantics while only acquiring exclusive locks on mutations.
 
 -- fn_ensure_table is a lock-friendly replacement for `CREATE TABLE IF NOT EXISTS`.
+-- WARNING: This function does not support uppercase names.
 --
 -- Example usage:
 --
@@ -30,6 +31,7 @@ END
 $func$;
 
 -- fn_ensure_column is a lock-friendly replacement for `ALTER TABLE ... ADD COLUMN IF NOT EXISTS`.
+-- WARNING: This function does not support uppercase names.
 --
 -- Example usage:
 --