Let CDB_CheckQuota second parameter override configured user quota

Closes #13
Includes automated test

test/CDB_QuotaTest.sql

@@ -1,6 +1,12 @@
 set client_min_messages to ERROR;
 \set VERBOSITY terse
 CREATE TABLE big(a int);
+-- Try the legacy interface
+-- See https://github.com/CartoDB/cartodb-postgresql/issues/13
+CREATE TRIGGER test_quota BEFORE UPDATE OR INSERT ON big
+      EXECUTE PROCEDURE CDB_CheckQuota(1,1);
+INSERT INTO big VALUES (1); -- allowed, check runs before
+INSERT INTO big VALUES (1); -- disallowed, quota exceeds before
 SELECT CDB_CartodbfyTable('big');
 INSERT INTO big SELECT generate_series(1,1024);
 SELECT CDB_SetUserQuotaInBytes(8);

test/CDB_QuotaTest_expect

@@ -1,5 +1,8 @@
 SET
 CREATE TABLE
+CREATE TRIGGER
+INSERT 0 1
+ERROR:  Quota exceeded by 3.9990234375KB
 
 INSERT 0 1024
 0