[DependencyInjection] Add exception for service name not dumpable in PHP
[DependencyInjection] Fix Container::camelize to convert beginning and ending chars

To convert a service ID exactly like Container::get
Merge branch '2.2' into 2.3

* 2.2:
  [Validator] fixed ConstraintViolation:: incorrect when nested
  handle Optional and Required constraints from XML or YAML sources correctly
  added missing comments to WebTestCase
  Fixed #8455: PhpExecutableFinder::find() does not always return the correct binary
  [DependencyInjection] Fix Container::camelize to convert beginning and ending chars
  [Validator] Fixed groups argument misplace for validateValue method from validator class

Conflicts:
	src/Symfony/Component/Validator/Tests/Constraints/CollectionTest.php
	src/Symfony/Component/Validator/Tests/GraphWalkerTest.php