Fixed bug in ChoiceType triggering a warning when not using utf-8

This fixes issue #10409 by not using json_encode anymore, but serialize
instead.
Added test case for 4c6a2d15095c13b2a35751b2b2712b183be489c4
fixed CS
[Form] Added check for parent disabled status in Button form elements

The Button form element did not check for the parent disabled configuration status,
making them behave differently to all other form widgets.
[Form] Added test for disabling buttons
Merge branch '2.3' into 2.4

* 2.3:
  Revert PHPUnit version, revert APC configuration
  removed APC on the CLI for Travis as it does not work well with PHPUnit and Composer anyway
  [Security] Replace exception mocks with actual exception instances.
  Remove an unused argument.
  Use `Filesystem::chmod` instead of `chmod` when dumping file
  [Form] Added test for disabling buttons
  [Form] Added check for parent disabled status in Button form elements
  Fixes URL validator to accept single part urls
  tweaked Travis configuration to get more tests running
  fixed float comparison in unit tests for HHVM
  upgraded PHPUnit to version 4 for better HHVM support
  [Process] fixed HHVM usage on the CLI
  Fix class names in ApcUniversalClassLoader tests.
  fixed the profiler when an uncalled listener throws an exception when instantiated
  fixed CS
  Added test case for 4c6a2d15095c13b2a35751b2b2712b183be489c4
  Fixed bug in ChoiceType triggering a warning when not using utf-8
  fixed CS
  Avoid levenshtein comparison when using ContainerBuilder.

Conflicts:
	src/Symfony/Component/Form/Extension/Core/Type/ChoiceType.php
	src/Symfony/Component/HttpKernel/Debug/TraceableEventDispatcher.php