[ADMB Users] ADMB and MinGW-w64 users should update

[dave fournier]

As I recall there were two issues involved with having a buffer size > 
2GB. First was
to use an 8 byte integer type for the offset.

The second issue was that if the buffer gets full it is saved to disk 
with a low level unbuffered
write. This write could not write more than 2GB  for me. Of course if 
the buffer is large
enough so that it never gets full that is not a problem.