[Form][RFC] added failing test for 'en_GB' locale and missing `ja_JP`

I was having some trouble with the list of locales available via the `LocaleType`.  When the default locale is `en_US` or `en_CA` it works as expected, but for `en_GB` the list has just one entry:

```php
array('tzm' => 'Central Morocco Tamazight')
```

Further, for `fr`, the list is correct, but for `fr_CA` it is not:

```php
array(
    'si' => 'singhalais',
    'to' => 'tongan'
)
```

Also, it appears the `ja_JP` locale is missing entirely.

I have wrote a some failing tests based on this issue.

```
There were 4 failures:

1) Symfony\Component\Form\Tests\Extension\Core\Type\LocaleTypeTest::testLocalesAreSelectable with data set #0 ('en')
Failed asserting that an array contains Symfony\Component\Form\Extension\Core\View\ChoiceView Object (
    'data' => 'ja_JP'
    'value' => 'ja_JP'
    'label' => 'Japanese (Japan)'
).

/home/kbond/www/symfony/src/Symfony/Component/Form/Tests/Extension/Core/Type/LocaleTypeTest.php:42

2) Symfony\Component\Form\Tests\Extension\Core\Type\LocaleTypeTest::testLocalesAreSelectable with data set #1 ('en_US')
Failed asserting that an array contains Symfony\Component\Form\Extension\Core\View\ChoiceView Object (
    'data' => 'ja_JP'
    'value' => 'ja_JP'
    'label' => 'Japanese (Japan)'
).

/home/kbond/www/symfony/src/Symfony/Component/Form/Tests/Extension/Core/Type/LocaleTypeTest.php:42

3) Symfony\Component\Form\Tests\Extension\Core\Type\LocaleTypeTest::testLocalesAreSelectable with data set #2 ('en_CA')
Failed asserting that an array contains Symfony\Component\Form\Extension\Core\View\ChoiceView Object (
    'data' => 'ja_JP'
    'value' => 'ja_JP'
    'label' => 'Japanese (Japan)'
).

/home/kbond/www/symfony/src/Symfony/Component/Form/Tests/Extension/Core/Type/LocaleTypeTest.php:42

4) Symfony\Component\Form\Tests\Extension\Core\Type\LocaleTypeTest::testLocalesAreSelectable with data set #3 ('en_GB')
Failed asserting that an array contains Symfony\Component\Form\Extension\Core\View\ChoiceView Object (
    'data' => 'en'
    'value' => 'en'
    'label' => 'English'
)
```