Description:
------------
As I was testing a script where I need to get the second day of previous month I 
found out this issue : I can't get this day with that phrase.
With larger tests I got the issue for every "ordinal" keyword apart from "first" 
and "last".

Test script:
---------------
date_default_timezone_set('Europe/Paris');
$firstDay = new DateTime('first day of previous month');
echo $firstDay->format('l').PHP_EOL;
$lastDay = new DateTime('last day of previous month');
echo $lastDay->format('l').PHP_EOL;
$secondDay = new DateTime('second day of previous month');
echo $secondDay->format('l').PHP_EOL;
$thirdDay = new DateTime('third day of previous month');
echo $thirdDay->format('l').PHP_EOL;

Expected result:
----------------
Sunday
Monday
Monday
Tuesday

Actual result:
--------------
Sunday
Monday
PHP Fatal error:  Uncaught exception 'Exception' with message 
'DateTime::__construct(): Failed to parse time string (second day of previous 
month) at position 11 (o): The timezone could not be found in the database' in 
/home/isen/essai.php:7
Stack trace:
#0 /home/isen/essai.php(7): DateTime->__construct('second day of p...')
#1 {main}
  thrown in /home/isen/essai.php on line 7

Fatal error: Uncaught exception 'Exception' with message 
'DateTime::__construct(): Failed to parse time string (second day of previous 
month) at position 11 (o): The timezone could not be found in the database' in 
/home/isen/essai.php:7
Stack trace:
#0 /home/isen/essai.php(7): DateTime->__construct('second day of p...')
#1 {main}
  thrown in /home/isen/essai.php on line 7