see patch #749830:

"""
This patch makes the UNIX mmap behave like the Windows
mmap in that if you pass 0 as the mmap size, the map
size will default to the current length of the file
being mmapped.

This allows avoids a call to os.stat if you want to map
the entire file. It also makes code using this feature
of the Windows mmap to be portable to UNIX.
"""

This new patch applies cleanly on current CVS HEAD.