mmap interface for windows

[cyrush]

On windows we don't have access to mmap, we have to use a windows specific API.

http://msdn.microsoft.com/en-us/library/aa366556%28VS.85%29.aspx

For now, i ifdef calls to mmap out on windows, and added an exception if someone tries this path.

[cyrush]

here is an example that is its more complex than we need, but I think includes the mechanics we are interested in:

http://stackoverflow.com/questions/1880714/createfilemapping-mapviewoffile-how-to-avoid-holding-up-the-system-memory

[cyrush]

resovled in #63