Description:
------------
IntlDateFormatter::parse() throws warnings on not parsable date.
This seems to happen only on Windows but should not happen according to the docs because return value of false is already sufficient indicator for the wrong date.

Originally reported here: https://github.com/yiisoft/yii2/issues/5962

Test script:
---------------
<?php

ini_set('display_errors', 1);
error_reporting(-1);

echo "PHP: " . PHP_VERSION . "\n";
echo "ICU: " . INTL_ICU_VERSION . "\n";

$formatter = new IntlDateFormatter('en_GB', IntlDateFormatter::MEDIUM, IntlDateFormatter::NONE, 'UTC');
// enable strict parsing to avoid getting invalid date values
$formatter->setLenient(false);
var_dump($formatter->parse('20121212'));

$formatter = new IntlDateFormatter('en_GB', IntlDateFormatter::NONE, IntlDateFormatter::NONE, 'UTC', null, 'yyyy.MM.dd');
// enable strict parsing to avoid getting invalid date values
$formatter->setLenient(false);
var_dump($formatter->parse('20121212'));


Expected result:
----------------
According to the docs there should not be a warning but only return value of false. 
http://php.net/manual/en/intldateformatter.parse.php
This is the case for Linux (at least my version).

Actual result:
--------------
Output on Windows:

PHP: 5.5.12 ICU: 51.2 
Warning: IntlDateFormatter::parse(): Date parsing failed in C:\wamp\www\CVCVMProperty\web\date-test.php on line 11
bool(false) 
Warning: IntlDateFormatter::parse(): Date parsing failed in C:\wamp\www\CVCVMProperty\web\date-test.php on line 16
bool(false)

Output on Linux (Ubuntu):

PHP: 5.4.35-1+deb.sury.org~precise+1
ICU: 4.8.1.1
bool(false)
bool(false)