to multi_runsingle() without it being really necessary or good

timeout'ed connections and possibly deal with them too

HAVE_WINDOWS_H, HAVE_WINSOCK_H, HAVE_WINSOCK2_H, neither
HAVE_WS2TCPIP_H when __CYGWIN__ is defined.

fast treatment of many simultaneous transfers

not always zero!

used anymore since multi->num_alive was introduced

Silence compiler warning 'unused parameter running_handles' in function multi_runsingle(). This is done here returning multi->num_alive in the running_handles parameter even when functions that call multi_runsingle() at this moment overwrite the returned value with the one that is valid when those functions curl_multi_perform() and multi_socket() have removed expired timers from the splay. Most probably, parameter 'running_handles' in function multi_runsingle() should be just removed.

*multi_socket*() can't return the proper number

if the header "Transfer-Encoding: chunked" was set by the application.
http://curl.haxx.se/bug/view.cgi?id=1531838

an unknown error number on glibc systems.
http://curl.haxx.se/bug/view.cgi?id=1532289

both now provide the number of running handles back to the calling function.

Winsock and Cygwin need address family specification before bind(), this should be harmless for others.