Description:
------------
If just a single letter is passed to the constructor of \DateTime it is accepted 
as a valid timezone string. Except, for some strange reason, the letter 'j'.

Test script:
---------------
$date = new \DateTime('a');
var_dump($date);

Expected result:
----------------
I expect an exception to be raised with the message:-

Fatal error: Uncaught exception 'Exception' with message 'DateTime::__construct(): 
Failed to parse time string (a) at position 0 (a): The timezone could not be found 
in the database' 

Actual result:
--------------
Except for when the letter 'j' is passed a DateTime object is created. For example 
the following code:-

$date = new \DateTime('a');
var_dump($date);

Will give the following output:-

object(DateTime)[1]
  public 'date' => string '2013-09-29 15:17:19' (length=19)
  public 'timezone_type' => int 2
  public 'timezone' => string 'A' (length=1)


Where it should raise an exception.