[TwigBundle] added support for custom loader paths

Before this commit, there was no ability to specify custom
search paths for Twig loader. Lets say we have twig templates
outside bundles directories (parts of the domain logic, not
application) - we want to be able to load them.

This commit adds `loader_paths` parameter to twig config,
which is used to set custom paths to the loader.
Update to the "Upgrade to v2.1" documentation: the way HTML attributes are passed for the `form_label` function has changed.
Simpler sentence concerning upgrade of the form_label function
[Form] Refactored processing of the "empty_value" option in DateType
merged branch michaelperrin/upgrade_to_21 (PR #4802)

Commits
-------

81eb722 Simpler sentence concerning upgrade of the form_label function
f6f1bb5 Update to the "Upgrade to v2.1" documentation: the way HTML attributes are passed for the `form_label` function has changed.

Discussion
----------

Update upgrade to 2.1 documentation concerning form_label

The way HTML attributes are passed for the `form_label` function has changed since this commit :
https://github.com/symfony/symfony/commit/167e64f79992f6366108fde1548e2a2c9552d3c6

I also made a PR for the documentation:
https://github.com/symfony/symfony-docs/pull/1542
merged branch everzet/twig-paths (PR #4649)

Commits
-------

dbeff69 [TwigBundle] added support for custom loader paths

Discussion
----------

[TwigBundle] added support for custom loader paths

Before this commit, there was no ability to specify custom
search paths for Twig loader. Lets say we have twig templates
outside bundles directories (parts of the domain logic, not
application) - we want to be able to load them.

This commit adds `loader_paths` parameter to twig config,
which is used to set custom paths to the loader.

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by travisbot at 2012-06-25T09:50:44Z

This pull request [passes](http://travis-ci.org/symfony/symfony/builds/1699654) (merged dbeff697 into 03c8d4d2).

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by vicb at 2012-06-26T06:14:30Z

You also need to support xml in the configuration and update the xsd file.

edit: adding some DI unit tests is probably a good idea.

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by everzet at 2012-06-26T08:49:20Z

@vicb agree, was just a fast stabbing ;)

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by fabpot at 2012-06-28T14:06:02Z

I'm +1. Can you "finish" the PR?

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by fabpot at 2012-07-02T13:23:33Z

@everzet If you don't have time, I can do the remaining work.
[TwigBundle] added a new paths setting to allow configuration of more paths for the filesystem loader (refs #4649)
[Form] Fixed display of empty values in DateType, TimeType and DateTimeType if they are not required
[Validator] fixed error message for dates like 2012-02-31 (closes #4223)
Merge branch '2.0'

* 2.0:
  [Validator] fixed error message for dates like 2012-02-31 (closes #4223)
merged branch bschussek/issue4596 (PR #4804)

Commits
-------

e6b5595 [Form] Fixed display of empty values in DateType, TimeType and DateTimeType if they are not required
14e293f [Form] Refactored processing of the "empty_value" option in DateType

Discussion
----------

[Form] Fixed display of empty values in DateType, TimeType and DateTimeType

Bug fix: yes
Feature addition: no
Backwards compatibility break: no
Symfony2 tests pass: yes
Fixes the following tickets: #4596
Todo: -