Bugfix: Cellblender viz output for Windows.

The visualization data generated by MCell in Windows (using CELLBLENDER
mode) could not be read by CellBlender. In Linux, it doesn't seem to
matter if one specifies "w" or "wb" when using fopen (via open_file) to
write binary data. However, for Windows, it needs to be explicitly set
("wb").

The formatting and indentation were also cleaned up slightly.