Add PostgreSQL version of SQLite integ tests

- Add PostgreSQL throwaway database
- Add optional length parameter for random string
- Fix syntax for PostgreSQL in several areas
- Add optional ID for whereById type determination

tests/unit/FieldTest.php

@@ -221,7 +221,7 @@ class FieldTest extends TestCase
         try {
             $field = Field::LE('le_field', 18, '@it');
             $field->qualifier = 'q';
-            $this->assertEquals("q.data->>'le_field' <= @it", $field->toWhere(),
+            $this->assertEquals("(q.data->>'le_field')::numeric <= @it", $field->toWhere(),
                 'WHERE fragment not generated correctly');
         } finally {
             Configuration::$mode = null;
@@ -248,7 +248,7 @@ class FieldTest extends TestCase
         Configuration::$mode = Mode::PgSQL;
         try {
             $field = Field::EQ('sub.foo.bar', 22, '@it');
-            $this->assertEquals("data->>'sub.foo.bar' = @it", $field->toWhere(),
+            $this->assertEquals("(data#>>'{sub,foo,bar}')::numeric = @it", $field->toWhere(),
                 'WHERE fragment not generated correctly');
         } finally {
             Configuration::$mode = null;