Add update + join support.

This currently only works in MySQL. Additional work will be needed to
make it work with postgres + sqlite.

lib/Cake/Database/Query.php

@@ -291,7 +291,7 @@ protected function _traverseDelete(callable $visitor) {
  * @return void
  */
 	protected function _traverseUpdate(callable $visitor) {
-		$parts = ['update', 'set', 'where'];
+		$parts = ['update', 'join', 'set', 'where'];
 		foreach ($parts as $name) {
 			call_user_func($visitor, $this->_parts[$name], $name);
 		}

lib/Cake/Test/TestCase/Database/QueryTest.php

@@ -1626,6 +1626,32 @@ public function testUpdateWithExpression() {
 		$this->assertCount(1, $result);
 	}
 
+/**
+ * Test updates with joins.
+ *
+ * @return void
+ */
+	public function testUpdateWithJoins() {
+		$query = new Query($this->connection);
+
+		$query->update('articles')
+			->set('title', 'New title')
+			->join([
+				'table' => 'authors',
+				'alias' => 'a',
+				'conditions' => 'author_id = a.id'
+			])
+			->where(['articles.id' => 1]);
+		$result = $query->sql(false);
+
+		$this->assertContains('UPDATE articles INNER JOIN authors a ON author_id = a.id', $result);
+		$this->assertContains('SET title = :', $result);
+		$this->assertContains('WHERE articles.id = :', $result);
+
+		$result = $query->execute();
+		$this->assertCount(1, $result);
+	}
+
 /**
  * You cannot call values() before insert() it causes all sorts of pain.
  *