change opening h323 logfile with append mode instead of overwrite

........

Merged revisions 370988 from http://svn.asterisk.org/svn/asterisk/branches/1.8
........

Merged revisions 370989 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@371010 65c4cc65-6c06-0410-ace0-fbb531ad65f3