Fix a problem with "svn log --diff" seen on Windows, ensure that
the log output comes before the diff output.

* subversion/svn/log-cmd.c (log_entry_receiver): Extra flush.


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/1.7.x-log-diff@1295671 13f79535-47bb-0310-9956-ffa450edef68