FTP: wait on both connections during active STOR state

When doing PORT and upload (STOR), this function needs to extract the
file descriptor for both connections so that it will respond immediately
when the server eventually connects back.

This flaw caused active connections to become unnecessary slow but they
would still often work due to the normal polling on a timeout. The bug
also would not occur if the server connected back very fast, like when
testing on local networks.

Bug: http://curl.haxx.se/bug/view.cgi?id=1183
Reported by: Daniel Theron