Working with files over 2GB in D2

[dsimcha]

Does anyone know how to work with huge (2GB+) files in D2?  std.stream has
overflow bugs (I haven't isolated them yet) and can't return their size
correctly, std.stdio.File throws a ConvOverflowError in seek() because fseek()
apparently takes an int when it should take a long, and std.file only supports
reading the whole file, which I can't do in 2GB address space.

It appears none of the file I/O on Phobos has been tested on huge files (until
now).