archiving fails when DumbBTree has to create new file

[Jtittsler]

In 2.0b3 Mailman/Archiver/HyperDatabase.py the DumbBTree() initialization
fails if the file specified does not exist. The error
passed back from open_ex always causes e.errno to be set
to None (rather than errno.ENOENT).

I didn't solve the problem, but just added a line before the try:
except: clause to avoid it.

     if not os.path.exists(path): return # e.errno below will be None
     try:
         fp = open(path)

[http://sourceforge.net/tracker/index.php?func=detail&aid=208837&group_id=103&atid=100103]

[Barry Warsaw (barry)]

Fixed for 2.0beta4