-# progress meter: avoid superfluous updates and duplicate lines

By comparing if a different "progress point" is reached or not since the
previous update, the progress function callback for this now avoids many
superfluous screen updates. This has the nice side-effect that it fixes
a problem that causes a second progress meter line.

The second line output happened because when we use the -# progress
meter, we force a newline output after the transfer in the main loop in
curl, but when libcurl calls the progress callback from
curl_easy_cleanup() it would then output the progress display
again. Possibly the naive newline output is wrong but this optimization
was suitable anyway...

Reported by: Daniel Theron
Bug: http://curl.haxx.se/bug/view.cgi?id=3517418