[DependencyInjection] Allow frozen containers to be dumped to graphviz
Merge branch '2.0' into 2.1

* 2.0:
  [DependencyInjection] Allow frozen containers to be dumped to graphviz
  Add dot character `.` to legal mime subtype regular expression
  [HttpFoundation] fixed the creation of sub-requests under some circumstancies (closes #6923, closes #6936)
[DependencyInjection] Add clone for resources which were introduced in 2.1