HTTP: reset expected DL/UL sizes on redirects

With FOLLOWLOCATION enabled. When a 3xx page is downloaded and the
download size was known (like with a Content-Length header), but the
subsequent URL (transfered after the 3xx page) was chunked encoded, then
the previous "known download size" would linger and cause the progress
meter to get incorrect information, ie the former value would remain
being sent in. This could easily result in downloads that were WAY
larger than "expected" and would cause >100% outputs with the curl
command line tool.

Test case 599 was created and it was used to repeat the bug and then
verify the fix.

Bug: http://curl.haxx.se/bug/view.cgi?id=3510057
Reported by: Michael Wallner