[Form] Simplified CSRF mechanism and removed "csrf" type

CSRF fields are now only added when the view is built. For this reason we already know if
the form is the root form and avoid to create unnecessary CSRF fields for nested fields.
[Form] Removed obsolete exceptions
[Form] Deprecated FieldType, which has been merged into FormType
[Form] Fixed regression: bind(null) was not converted to an empty string anymore
merged branch bschussek/issue3878 (PR #3923)

Commits
-------

6e4ed9e [Form] Fixed regression: bind(null) was not converted to an empty string anymore
fcb2227 [Form] Deprecated FieldType, which has been merged into FormType
bfa7ef2 [Form] Removed obsolete exceptions
2a49449 [Form] Simplified CSRF mechanism and removed "csrf" type

Discussion
----------

[Form] Merged FieldType into FormType

Bug fix: no
Feature addition: no
Backwards compatibility break: yes
Symfony2 tests pass: yes
Fixes the following tickets: #3878
Todo: update the documentation on theming

![Travis Build Status](https://secure.travis-ci.org/bschussek/symfony.png?branch=issue3878)

This PR is a preparatory PR for #3879. See also #3878.

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by juliendidier at 2012-04-13T14:25:19Z

What's the benefit ?

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by henrikbjorn at 2012-04-13T14:26:40Z

why `input_widget` ? and not just `widget`

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by Burgov at 2012-04-13T14:27:49Z

@juliendidier dynamic inheritance is now obsolete which fixes some other issues

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by stloyd at 2012-04-13T14:37:26Z

What about __not__ breaking API so *badly* and leaving `FieldType` which will be simple like (with marking as deprecated):

```php
<?php

class FieldType extends AbstractType
{
    public function getParent(array $options)
    {
        return 'form';
    }

    public function getName()
    {
        return 'field';
    }
}

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by bschussek at 2012-04-13T14:43:41Z

@stloyd That's a very good idea.

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by mvrhov at 2012-04-13T17:41:21Z

IMHO what @stloyd proposed sounds like a good idea, but removing FieldType class, if #3903 will come into life might ensure that more forms will broke and people will check them thoroughly.

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by r1pp3rj4ck at 2012-04-13T18:46:08Z

@bschussek looks great, but I'm concerned about how quickly will the third-party bundles adapt to this BC break. I hope really quick, because if they don't the whole stuff will be useless :S of course it's not your problem to solve.

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by stof at 2012-04-13T18:50:32Z

@r1pp3rj4ck there is already another BC break requiring to update custom types for Symfony master. So third party bundles already have to do some work.

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by r1pp3rj4ck at 2012-04-13T18:59:37Z

@stof which one? I've looked into @bschussek 's RFC about these [foo].bar stuff, but it's not yet implemented. Are you refering to this or another one I've missed?

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by stof at 2012-04-13T19:04:06Z

@r1pp3rj4ck the change regarding default options

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by r1pp3rj4ck at 2012-04-13T19:06:10Z

@stof oh, I forgot that one. Weird thing is that I've already changed my default options today and still forgetting these stuff :D

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by bschussek at 2012-04-14T08:58:29Z

I restored and deprecated FieldType now. I'd appreciate further reviews.

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by stloyd at 2012-04-14T09:02:32Z

Maybe we should try to avoid this BC in templates ? What do you think about similar move like with `FieldType` ? (hold old, but inside just render new)

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by bschussek at 2012-04-14T09:07:22Z

@stloyd You mean for those cases where people explicitely render the block "field_*"? We can do that.

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by stloyd at 2012-04-14T09:09:45Z

@bschussek Yes I mean this case =) Sorry for not being explicit, I need some coffee I think =)

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by bschussek at 2012-04-17T14:45:35Z

I added the field_* blocks again for BC. Could someone please review again? Otherwise this can be merged.

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by Burgov at 2012-04-17T15:11:16Z

@bschussek I'm not sure what has changed to cause this, but if I try out your branch on our forms, if I leave the value of an input empty, eventually the reverseTransform method receives a null value, rather than a '' (empty string) value, as on the current symfony master.

DateTimeToLocalizedStringTransformer, for example, will throw an Exception if the value is not a string

```php
if (!is_string($value)) {
   throw new UnexpectedTypeException($value, 'string');
}
```

Other than that, all forms render just the same as they do on symfony master

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by bschussek at 2012-04-17T15:30:29Z

@Burgov Fixed.