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I have update the patch (mmap3.diff) for the current trunk
(52498).
I've reviewed and tested the Windows implementation, and found
the original patch to be incorrect: For MapViewOfFile,
instead of
passing the size, offset+size must be passed. I also extended it
to support 64-bit offsets on a 64-bit system (64-bit offsets on
a 32-bit system still aren't supported).

I have doubts about the changes to find and tell: why is it
good that it includes the offset? In particular, for find,
I think it should return the index in the buffer, not the
offset in the file.