The fix for QFJ-318 was reverted (inadvertently?) in r928

We've found that the components (timestamp, message, newline) of log lines are occasionally interleaved in multi-threaded applications that concurrently send and receive FIX messages via QuickFIX/J 1.5.2. This issue wasn't present in QuickFIX/J 1.3.2.
It looks to me like the removal of "synchronized" from FileLog.writeMessage() in r928 was an error. None of the JIRA tickets cited in the commit log seem to explain the change.