[Process] Use assertSame instead of assertEquals to avoid comparison against `null`
[Process] Fix process status in TTY mode

When running a process with TTY mode, status in automatically set to `terminated`
once it's started.

It's wrong for two reasons :
 - The status of the process is not yet terminated.
 - The exitcode value is never caught
bug #10412 [Process] Fix process status in TTY mode (romainneutron)

This PR was merged into the 2.3 branch.

Discussion
----------

[Process] Fix process status in TTY mode

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| License       | MIT

When running a process with TTY mode, status in automatically set to `terminated`
once it's started.

It's wrong for two reasons :
 - The status of the process is not yet terminated.
 - The exitcode value is never caught

Commits
-------

51c70f8 [Process] Fix process status in TTY mode
[Process] Make process tests more accurate on exception messages
[Process] Fix some unit tests that create the process object instead of delegate it to the implementation
[Process] Fix #9160 : escaping an argument with a trailing backslash on windows fails
Merge branch '2.3' into 2.4

* 2.3:
  [Process] Fix #9160 : escaping an argument with a trailing backslash on windows fails
  [Process] Fix some unit tests that create the process object instead of delegate it to the implementation
  [Process] Make process tests more accurate on exception messages
  [Process] Fix process status in TTY mode
  [Process] Use assertSame instead of assertEquals to avoid comparison against `null`
  [HttpFoundation] added some unit tests
  10158 get vary multiple
  made Cookie stringification more robust
  [Yaml] fix for a HHVM bug