logo header layout

I looked at the logo file from the RLN36 (the file `logo`). The file contains a header, with two JPEG files. This is what I *think* the logo layout looks like:

```
0-3: magic
4-7: total length of file
8-11: unknown
12-15: offset of first JPEG
16-19: offset of second JPEG
20-23: length of first JPEG
24-27: length of second JPEG
28-31: unknown (all NUL bytes) 
```