[ticket/12388] Fix translation of log entries without additional log data

PHPBB3-12388
[ticket/12388] Add tests for lang() use on log actions without data

PHPBB3-12388
[ticket/8960] Allow changing avatar path if it's not writable

This change will allow users to change the avatar path even if it's not
writable. However, this will get rid of the error message that the path is
not writable. Due to this, a minor addition to the explain message in the ACP
settings has been made.

PHPBB3-8960
Merge pull request #2286 from nickvergessen/ticket/12388

[ticket/12388] Fix translation of log entries without additional log data

* nickvergessen/ticket/12388:
  [ticket/12388] Add tests for lang() use on log actions without data
  [ticket/12388] Fix translation of log entries without additional log data
Merge branch 'ticket/8960-olympus' into ticket/8960

Conflicts:
	phpBB/includes/acp/acp_board.php