[Routing] serialize the compiled route to speed things up

This also makes the CompiledRoute implement Serializable in order to:
1. make the serialization format shorter
2. have no null bytes in there, which the native serializer add for private properties, and thus would complicate saving in databases etc.
3. We should add to our symfony BC promise, that only classes that implement Serializable are ensured to be deserializable correctly with serialized representations of the class in previous symfony versions.
Merge branch '2.3' into 2.5

* 2.3:
  added missing files
  [TwigBundle] added a test
  Indicate which file was being parsed if an exception is thrown while running translation:debug
  [ClassLoader] Cast $useIncludePath property to boolean
  [HttpFoundation] Minor spelling fix in PHPDocs
  improve error message for multiple documents
  [Session] remove invalid workaround in session regenerate
  [Kernel] ensure session is saved before sending response
  [Routing] serialize the compiled route to speed things up
  [Validator] Fixed Regex::getHtmlPattern() to work with complex and negated patterns
  [DependencyInjection] use inheritdoc for loaders
  [Config] fix filelocator with empty name
  [Form] fix form handling with unconventional request methods like OPTIONS
  CSRF warning docs on Request::enableHttpMethodParameterOverride()

Conflicts:
	src/Symfony/Component/Routing/Route.php