Make it possible to ctrl-c break out of transfer function

[raacampbell]

The transfer function failed recently because of a server problem: it claimed the destination is full and stops. Hack is to retry the transfer up to 20 times. This works but then if you want to quit you have to ctrl-c 20 times. The BASH error code for ctrl-c is 2. I don't know what the error code is when the transfer fails due to the claimed space problem. If it's not 2 then we can bail out with ctrl-c right away, which would be nice. Should try rsync to a full USB stick and see what the code is.