[MonologBridge] Ignore empty context/extra by default in the ConsoleFormatter
[Form] Added "label_format" option
[Validator] Made it possible to store the cause of a constraint violation
[Intl] Integrated ICU data into Intl component
[Debug] expose object_handle
updated CHANGELOG for 2.3.20
update CONTRIBUTORS for 2.3.20
updated VERSION for 2.3.20
bumped Symfony version to 2.3.21
updated CHANGELOG for 2.5.5
updated VERSION for 2.5.5
bumped Symfony version to 2.5.6
[Validator] Update validators.zh_CN.xlf, fix translation error
minor #12070 [Validator] Update validators.zh_CN.xlf, fix translation error (michaeljayt)

This PR was submitted for the master branch but it was merged into the 2.3 branch instead (closes #12070).

Discussion
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[Validator] Update validators.zh_CN.xlf, fix translation error

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets |
| License       | MIT
| Doc PR        |

Commits
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ab5aaab [Validator] Update validators.zh_CN.xlf, fix translation error
[HttpFoundation] remove base64 encoding of session data
[HttpFoundation] implement lazy connect for pdo session handler
add test for null byte in session data
[HttpFoundation] allow different lifetime per session
[HttpFoundation] add create table method to pdo session handler
added upgrade and changelog notes for PdoSessionHandler