Win32 fixes

The tests on Windows will fail if you have the EVENT_NOWIN32 environment variable set. Maybe it makes sense to turn off the check for this on windows, since then there will be no backend available at all?

Also fixed compilation of https-client.c

Right now there's some problem with the IOCP tests. I'm not sure if this is a regression.

```
iocp/port: [forking] OK
iocp/evbuffer: [forking] OK
iocp/bufferevent_async: [forking] OK
iocp/bufferevent/bufferevent: [forking] OK
iocp/bufferevent/bufferevent_watermarks: [forking] OK
iocp/bufferevent/bufferevent_filters: [forking] OK
iocp/bufferevent/bufferevent_connect: [forking] [warn] Unexpected error on AcceptEx: The I/O operation has been aborted because of either a thread exit or an application request.
[warn] Unexpected error on AcceptEx: The I/O operation has been aborted because of either a thread exit or an application request.
OK
iocp/bufferevent/bufferevent_connect_defer: [forking] OK
iocp/bufferevent/bufferevent_connect_lock: [forking] [warn] Unexpected error on AcceptEx: The I/O operation has been aborted because of either a thread exit or an application request.
OK
iocp/bufferevent/bufferevent_connect_lock_defer: [forking] OK
iocp/bufferevent/bufferevent_connect_fail: [forking]
  [bufferevent_connect_fail FAILED]
iocp/bufferevent/bufferevent_connect_nonblocking: [forking] [warn] Unexpected error on AcceptEx: The I/O operation has been aborted because of either a thread exit or an application request.
OK
iocp/listener/randport: [forking] OK
iocp/listener/error: [forking] OK
ssl/bufferevent_socketpair: [forking]
  WARN ..\test\regress_ssl.c:167: Version mismatch for openssl: compiled with 10
00105f but running with 1000005fOK
ssl/bufferevent_filter: [forking]
  WARN ..\test\regress_ssl.c:167: Version mismatch for openssl: compiled with 10
00105f but running with 1000005fOK
ssl/bufferevent_renegotiate_socketpair: [forking]
  WARN ..\test\regress_ssl.c:167: Version mismatch for openssl: compiled with 10
00105f but running with 1000005fOK
ssl/bufferevent_renegotiate_filter: [forking]
  WARN ..\test\regress_ssl.c:167: Version mismatch for openssl: compiled with 10
00105f but running with 1000005fOK
ssl/bufferevent_socketpair_startopen: [forking]
  WARN ..\test\regress_ssl.c:167: Version mismatch for openssl: compiled with 10
00105f but running with 1000005fOK
ssl/bufferevent_filter_startopen: [forking]
  WARN ..\test\regress_ssl.c:167: Version mismatch for openssl: compiled with 10
00105f but running with 1000005fOK
ssl/bufferevent_connect: [forking]
  WARN ..\test\regress_ssl.c:167: Version mismatch for openssl: compiled with 10
00105f but running with 1000005fOK
1/229 TESTS FAILED. (15 skipped)
```

From release-2.1.1-alpha (old nmake build):

```
iocp/port: [forking]
  FAIL regress_iocp.c:68: assert(count_cond)
  FAIL regress_i
  [port FAILED]
iocp/evbuffer: [forking]
  FAIL regress_iocp.c:68: assert(count_cond)
  FAIL regress_iocp.c:263: assert(!event_iocp_port_associate_(port, data->pair[0
], 100))
  [evbuffer FAILED]
iocp/bufferevent_async: [forking] [warn] event_add: event has no event_base set.

[warn] event_add: event has no event_base set.

  [bufferevent_async FAILED]
iocp/bufferevent/bufferevent: [forking] OK
iocp/bufferevent/bufferevent_watermarks: [forking] OK
iocp/bufferevent/bufferevent_filters: [forking] OK
iocp/bufferevent/bufferevent_connect: [forking] [warn] Unexpected error on Accep
tEx: Unknown error
OK
iocp/bufferevent/bufferevent_connect_defer: [forking] OK
iocp/bufferevent/bufferevent_connect_lock: [forking] [warn] Unexpected error on
AcceptEx: Unknown error
OK
iocp/bufferevent/bufferevent_connect_lock_defer: [forking] OK
iocp/bufferevent/bufferevent_connect_fail: [forking] OK
iocp/bufferevent/bufferevent_connect_nonblocking: [forking] [warn] fcntl(200, F_
GETFL): Socket operation on nonsocket [WSAENOTSOCK ]
OK
iocp/listener/randport: [forking] OK
iocp/listener/error: [forking] OK
3/184 TESTS FAILED. (15 skipped)
```