Overall overage transfer speed

[bigntallmike]

While watching a few thousand files copy from a memory card with -g I was wishing there was an overall average speed display on the top progress bar, to go along with the per-file speed on the lower one.
I may even have a look at implementing it myself at some point, but I thought I'd mention it here first.

[bigntallmike]

It was easy enough and I've added that functionality on my own fork instead.