merge the stat and data records

This works, and it improves TestPerf's "time to access another file" significantly (because it cuts the number of transactions in half):

> Time to open file: 30ms
> Time to create file: 2ms
> Time to write/flush to output stream: 180ms
> Time to close output stream: 3ms
> Time to delete file: 48ms
> Time to close file: 1ms
> Time to reopen file: 1ms
> Time to access another file: 4907ms

But I want to think about further improvements a bit before we merge it, so I'm marking it WIP.

Note: this is based on the fs-perf branch, so it'll show a bunch of additional changes until that branch is merged.
The JSR-075 documentation doesn't say much about *rename*:
> Renames the selected file or directory to a new name in the same directory. The file or directory is renamed immediately on the actual file system upon invocation of this method. No file or directory by the original name exists after this method call. All previously open input and output streams are automatically flushed and closed. Attempts to further use those streams result in an IOException. The FileConnection instance object remains open and available for use, referring now to the file or directory by its new name.

The C native uses the MoveFile function (http://msdn.microsoft.com/en-us/library/windows/desktop/aa365239%28v=vs.85%29.aspx)