download of image fails

[lonetech]

Presumably there's a limit to how large a transfer can be requested through SG, and 16MB is over it. Downloader class already supports chunked download, so I just need to communicate the limit.

[lonetech]

That's not the full story. While I found the limit, and it's 32KiB, download picture commands don't seem to respond immediately, while download file commands do.

[lonetech]

Widening the issue. I have now tested all three protocol implementations, USB fails by not recognizing when the camera hasn't yet loaded the next block, and IP fails at checking a response magic number. Fixable for certain, but not yet cleaned up.