Use isset() instead of array_key_exists() in DIC
Merge branch '2.3'

* 2.3:
  Fixing singular form for kisses, accesses and addresses.
  fixed some circular references
  [Security] fixed a leak in ExceptionListener
  [Security] fixed a leak in the ContextListener
  Ignore posix_istatty warnings
  removed unused variable
  [Form] fix iterator typehint
  typos
  Button missing getErrorsAsString() fixes #8084 Debug: Not calling undefined method anymore. If the form contained a submit button the call would fail and the debug of the form wasn't possible. Now it will work in all cases. This fixes #8084
  Use isset() instead of array_key_exists() in DIC
  Fixed annotation
  [BrowserKit] fixed method/files/content when redirecting a request
  [BrowserKit] removed some headers when redirecting a request
  [BrowserKit] fixed headers when redirecting if history is set to false (refs #8697)
  [HttpKernel] fixed route parameters storage in the Request data collector (closes #8867)
  [BrowserKit] Pass headers when `followRedirect()` is called
  Return BC compatibility for `@Route` parameters and default values

Conflicts:
	src/Symfony/Component/Security/Http/Firewall/ContextListener.php