Do not enable DDL triggers on extension create

Use cartodb.cdb_enable_ddl_hooks() to enable them.
Closes #19

cartodb_hooks.sql

@@ -184,4 +184,5 @@ CREATE OR REPLACE FUNCTION cartodb.cdb_enable_ddl_hooks() returns void AS $$
     ON "column_add" EXECUTE PROCEDURE cartodb.cdb_handle_add_column();
 $$ LANGUAGE sql;
 
-SELECT cartodb.cdb_enable_ddl_hooks();
+-- Do not enable hooks by default
+--SELECT cartodb.cdb_enable_ddl_hooks();

expected/test_ddl_triggers.out

@@ -6,6 +6,18 @@ SELECT CDB_SetUserQuotaInBytes(0);
                        0
 (1 row)
 
+-- Enable ddl triggers
+SELECT cartodb.cdb_enable_ddl_hooks();
+NOTICE:  event trigger "cdb_on_relation_create" does not exist, skipping
+NOTICE:  event trigger "cdb_on_relation_drop" does not exist, skipping
+NOTICE:  event trigger "cdb_on_alter_column" does not exist, skipping
+NOTICE:  event trigger "cdb_on_drop_column" does not exist, skipping
+NOTICE:  event trigger "cdb_on_add_column" does not exist, skipping
+ cdb_enable_ddl_hooks 
+----------------------
+ 
+(1 row)
+
 create schema c;
 CREATE USER cartodb_postgresql_unpriv_user;
 GRANT ALL ON SCHEMA c to cartodb_postgresql_unpriv_user;

sql/test_ddl_triggers.sql

@@ -3,6 +3,9 @@
 -- Set user quota to infinite
 SELECT CDB_SetUserQuotaInBytes(0);
 
+-- Enable ddl triggers
+SELECT cartodb.cdb_enable_ddl_hooks();
+
 create schema c;
 
 CREATE USER cartodb_postgresql_unpriv_user;