fix axes handling in Crawler::filterXPath()

Due to some limitations in the relativize() method, it was not
possible to use XPath axes other than descendant or descendant-or-self
in the filterXPath() method of the Crawler class. This commit adds
support for the ancestor, ancestor-or-self, attribute, child,
following, following-sibling, parent, preceding, preceding-sibling and
self axes.
Merge branch '2.3' into 2.4

* 2.3: (22 commits)
  Fix incorrect romanian plural translations
  fix axes handling in Crawler::filterXPath()
  fix some docblocks
  Fixed self-reference in 'service_container' service breaks garbage collection (and clone).
  [Process] Fix tests when pcntl is not available.
  [DependencyInjection] Roll back changes made to generated files.
  [Console] Roll back changes made to fixture files.
  [Validator] Added more detailed inline documentation
  [Validator] Removed information from the violation output if the value is an array, object or resource
  partially reverted previous commit
  fixed CS
  properly handle null data when denormalizing
  [Validator] Renamed valueToString() to formatValue(); added missing formatValue() calls
  [Validator] Fixed CS
  [Validator] Fixed date-to-string conversion tests to match ICU 51
  [Validator] Added "{{ value }}" parameters where they were missing
  [Validator] Simplified and explained the LuhnValidator
  [Validator] Simplified IssnValidator
  [Validator] Fixed and simplified IsbnValidator
  [Validator] Simplified IBAN validation algorithm
  ...

Conflicts:
	src/Symfony/Component/Console/Helper/DescriptorHelper.php
	src/Symfony/Component/DependencyInjection/Container.php
	src/Symfony/Component/DomCrawler/Tests/CrawlerTest.php
	src/Symfony/Component/HttpFoundation/File/UploadedFile.php
	src/Symfony/Component/HttpKernel/Fragment/FragmentHandler.php
	src/Symfony/Component/Validator/Constraints/AbstractComparisonValidator.php
	src/Symfony/Component/Validator/Constraints/CollectionValidator.php
	src/Symfony/Component/Validator/Tests/Constraints/EqualToValidatorTest.php
	src/Symfony/Component/Validator/Tests/Constraints/GreaterThanValidatorTest.php
	src/Symfony/Component/Validator/Tests/Constraints/IdenticalToValidatorTest.php
	src/Symfony/Component/Validator/Tests/Constraints/LessThanOrEqualValidatorTest.php
	src/Symfony/Component/Validator/Tests/Constraints/LessThanValidatorTest.php
	src/Symfony/Component/Validator/Tests/Constraints/NotEqualToValidatorTest.php
	src/Symfony/Component/Validator/Tests/Constraints/NotIdenticalToValidatorTest.php