Description:
------------
If the format only includes a day string ('D' or 'l'), it is ignored, and a 
DateTime instance for the current date/time is returned. Maybe I'm a stupid idiot, 
but I would expect either an error, or for it to return a DateTime object for the 
next occurrence of the given day (similar to \DateTime::__construct('Monday');)

Test script:
---------------
<?php                                                                                                  
                                                                                                       
$date = new \DateTime('tomorrow');                                                                     
$date2 = \DateTime::createFromFormat('D', $date->format('D'));                                         
                                                                                                       
var_dump($date);                                                                                       
var_dump($date->format('D'));                                                                          
var_dump($date2);                                                                                      
var_dump($date2->format('D'));

Expected result:
----------------
I expect the same date/day to be selected in both cases.

Actual result:
--------------
object(DateTime)#1 (3) {
  ["date"]=>
  string(19) "2011-05-19 00:00:00"
  ["timezone_type"]=>
  int(3)
  ["timezone"]=>
  string(16) "America/New_York"
}
string(3) "Thu"
object(DateTime)#2 (3) {
  ["date"]=>
  string(19) "2011-05-18 18:49:33"
  ["timezone_type"]=>
  int(3)
  ["timezone"]=>
  string(16) "America/New_York"
}
string(3) "Wed"