Add Validator::hasField()

This will be useful in form building as fields without validation sets
should not default to required.

src/Validation/Validator.php

@@ -112,6 +112,16 @@ public function field($name, ValidationSet $set = null) {
 		return $this->_fields[$name];
 	}
 
+/**
+ * Check whether or not a validator contains any rules for the given field.
+ *
+ * @param string $name The field name to check.
+ * @return boolean
+ */
+	public function hasField($name) {
+		return isset($this->_fields[$name]);
+	}
+
 /**
  * Associates an object to a name so it can be used as a provider. Providers are
  * objects or class names that can contain methods used during validation of for

tests/TestCase/Validation/ValidatorTest.php

@@ -50,9 +50,12 @@ public function testAddingRulesToField() {
  */
 	public function testFieldDefault() {
 		$validator = new Validator;
+		$this->assertFalse($validator->hasField('foo'));
+
 		$field = $validator->field('foo');
 		$this->assertInstanceOf('\Cake\Validation\ValidationSet', $field);
 		$this->assertCount(0, $field);
+		$this->assertTrue($validator->hasField('foo'));
 	}
 
 /**