Merge branch '3.4' into 4.0

* 3.4:
  [HttpFoundation] Use the correct syntax for session gc based on Pdo driver
  Removed assertDateTimeEquals() methods.
  Revert "bug #24987 [Console] Fix global console flag when used in chain (Simperfit)"
  Revert "bug #25487 [Console] Fix a bug when passing a letter that could be an alias (Simperfit)"
  Disable CSP header on exception pages only in debug
  Fixed submitting disabled buttons
  Fixed Button::setParent() when already submitted
  Improve assertions
  Restore RoleInterface import
  [Console] Provide a bugfix where an array could be passed
  Improve assertions
  SCA: get rid of repetitive calls
  allow null values for root nodes in YAML configs
  revert useless tests fixtures changes
  [VarDumper] Fix docblock
  Improve phpdoc to make it more explicit
  [DI] Fix initialization of legacy containers by delaying include_once

Author: fabpot