add preferred_query option to ModelType

This enables the ModelChoiceList to use 'preferred_choices' of the parent ChoiceType.
use preferred_choices in favor of preferred_query
Merge branch '2.0' into 2.1

* 2.0:
  updated license year
  Update src/Symfony/Component/HttpFoundation/Response.php
  [Console] fixed unitialized properties (closes #5935)
  [Bundle] [FrameworkBundle] fixed typo in phpdoc of the SessionListener.
  bumped Symfony version to 2.0.21-DEV
  updated VERSION for 2.0.21
  updated CHANGELOG for 2.0.21

Conflicts:
	src/Symfony/Bundle/SwiftmailerBundle/LICENSE
	src/Symfony/Component/Filesystem/LICENSE
	src/Symfony/Component/HttpFoundation/Response.php
	src/Symfony/Component/HttpKernel/Kernel.php
Merge branch '2.1'

* 2.1: (24 commits)
  updated license year
  Update src/Symfony/Component/HttpFoundation/Response.php
  [Form] Fixed inheritance of "error_bubbling" in RepeatedType
  [Form] Fixed DateType when used with the intl extension disabled.
  [HttpFoundation] fix return types and handling of zero in Response
  [HttpFoundation] better fix for non-parseable Expires header date
  Fixed missing plural message in portuguese validator
  Fix Expires when the header is -1
  [DoctrineBridge] Allowing memcache port to be 0 to support memcache unix domain sockets.
  [Console] fixed unitialized properties (closes #5935)
  [Process] Prevented test from failing when pcntl extension is not enabled.
  Revert "[DoctrineBridge] Improved performance of the EntityType when used with the "query_builder" option"
  [Form] Fixed failing tests for DateTimeToStringTransformer.
  [Locale] Fixed the StubLocaleTest for ICU versions lower than 4.8.
  [Bundle] [FrameworkBundle] fixed typo in phpdoc of the SessionListener.
  [Form] Fixed test regression introduced in #6440
  [Tests] Fix namespaces
  Fixed php doc of GenericEvent::__construct
  HttpUtils must handle RequestMatcher too
  use preferred_choices in favor of preferred_query
  ...

Conflicts:
	src/Symfony/Bridge/Propel1/Form/ChoiceList/ModelChoiceList.php