Unit tests in Windows and a Windows timeout fix
This commit gets our unit tests compiling and running on Windows as well as removes a duplicated `timeval` -> `DWORD` conversion logic in sockcompat.c
There are minor differences in behavior between Linux and Windows to note:
1. In Windows, opening a non-existent hangs forever in WSAPoll whereas
it correctly returns with a "Connection refused" error on Linux.
For that reason, I simply skip this test in Windows.
It may be related to this known issue:
https://daniel.haxx.se/blog/2012/10/10/wsapoll-is-broken/
2. Timeouts are handled slightly differently in Windows and Linux.
In Linux, we intentionally set REDIS_ERR_IO for connection
timeouts whereas in Windows we set REDIS_ERR_TIMEOUT. It may be
prudent to fix this discrepancy although there are almost certainly
users relying on the current behavior.
