[ticket/11775] Fix error when moving the last post to another topic

PHPBB3-11775
[ticket/11775] Backport moving of the posting functions to 3.0

PHPBB3-11775
[ticket/11775] Add functional test for moving the last post

PHPBB3-11775
[ticket/11775] Split test into multiple steps

PHPBB3-11775
[ticket/11775] Remove spaces at line ends

PHPBB3-11775
[ticket/11775] Fix doc blocks syntax

PHPBB3-11775
Merge remote-tracking branch 'nickvergessen/ticket/11775' into prep-release-3.0.12

* nickvergessen/ticket/11775:
  [ticket/11775] Fix doc blocks syntax
  [ticket/11775] Remove spaces at line ends
  [ticket/11775] Split test into multiple steps
  [ticket/11775] Add functional test for moving the last post
  [ticket/11775] Backport moving of the posting functions to 3.0
  [ticket/11775] Fix error when moving the last post to another topic