Merge pull request #2784 from Nicofuma/ticket/11480-ascraeus

 [ticket/11480-ascraeus] PM : "Unknown folder" returned when inbox folder is full

* Nicofuma/ticket/11480-ascraeus:
  [ticket/11480] Header file
  [ticket/11480] Fix unit tests
  [ticket/11480] Move the test into get_folder()
  [ticket/11480] Fix the double spaces in phpbb_functional_test_case
  [ticket/11480] Fix typos
  [ticket/11480] Add functionnal test
  [ticket/11480] PM : "Unknown folder" returned when inbox folder is full
Merge branch 'develop-olympus' into develop-ascraeus

* develop-olympus: