Extremely slow Petrel import + crash when saving

[Henrik Brautaset Aronsen]

Jef Driesen wrote:
> Can you try the attached patch on your mac? Because sending data 
> appears to be the problem, sending the packet byte by byte is 
> certainly not going to be the fastest. With the attached patch, the 
> packet is send at once.
>
> Another thing that's worth looking at are the tcdrain calls in 
> serial_write. Just add some extra WARNING or INFO between the write 
> and tcdrain. I wonder if it's the write or the tcdrain which taking 
> most of the time.

Massive improvement!   The whole download process took 4.5 minutes, 
that's about 4.7 seconds per dive.  Thanks a lot!

Henrik