multi: remove_handle: move pending connections

If the handle removed from the multi handle happens to be the one
"owning" the pipeline other transfers will be waiting indefinitely. Now
we move such handles back to connect to have them race (again) for
getting the connection and thus avoid hanging.

Bug: http://curl.haxx.se/bug/view.cgi?id=1465
Reported-by: Jiri Dvorak