In trying to use the mmap offset to allow me to work with a 12GB file, I 
encountered the fact that the new offset parameter was a ssize_t, which 
is only 32 bits on my platform (OS X).  The mmap offset in C is defined 
to be an off_t 
(http://opengroup.org/onlinepubs/007908775/xsh/mmap.html), which is 64 
bits on my platform.  The attached patch attempts to fix the non-Windows 
code to have an off_t offset parameter and allows my code to access all 
12 GB of my file.  As a warning, this is the first time I've even looked 
at the Python source, and wouldn't even consider myself a Python coder; 
I just use Python every few months.  Review the patch carefully.