Fix issue with postgres and virtualFields

If a virtualField was set to a literal value it would be quoted.
Test added.

Fixes #2085

lib/Cake/Model/Datasource/Database/Postgres.php

@@ -394,6 +394,7 @@ public function fields($model, $alias = null, $fields = array(), $quote = true)
 
 /**
  * Auxiliary function to quote matched `(Model.fields)` from a preg_replace_callback call
+ * Quotes the fields in a function call.
  *
  * @param string $match matched string
  * @return string quoted strig
@@ -404,9 +405,11 @@ protected function _quoteFunctionField($match) {
 			$prepend = 'DISTINCT ';
 			$match[1] = trim(str_replace('DISTINCT', '', $match[1]));
 		}
-		if (strpos($match[1], '.') === false) {
+		$constant = preg_match('/^\d+|NULL|FALSE|TRUE$/i', $match[1]);
+
+		if (!$constant && strpos($match[1], '.') === false) {
 			$match[1] = $this->name($match[1]);
-		} else {
+		} elseif (!$constant){
 			$parts = explode('.', $match[1]);
 			if (!Set::numeric($parts)) {
 				$match[1] = $this->name($match[1]);

lib/Cake/Test/Case/Model/Datasource/Database/PostgresTest.php

@@ -751,6 +751,25 @@ public function testVirtualFields() {
 		$this->assertEqual($result['Article']['subquery'], 6);
 	}
 
+/**
+ * Test that virtual fields work with SQL constants
+ *
+ * @return void
+ */
+	function testVirtualFieldAsAConstant() {
+		$this->loadFixtures('Article', 'Comment');
+		$Article =& ClassRegistry::init('Article');
+		$Article->virtualFields = array(
+			'empty' => "NULL",
+			'number' => 43,
+			'truth' => 'TRUE'
+		);
+		$result = $Article->find('first');
+		$this->assertNull($result['Article']['empty']);
+		$this->assertTrue($result['Article']['truth']);
+		$this->assertEquals(43, $result['Article']['number']);
+	}
+
 /**
  * Tests additional order options for postgres
  *