Use CreateEventW instead of CreateEvent

[Kim Gräsman <kim.grasman@…>]

We use boost.asio together with the Poco library.

Poco has decided to #undef some common Windows API wrappers to avoid weird symbol decoration, among them CreateEvent.

The Windows convention is to have a #define for Function, which expands to FunctionA for non-Unicode builds and FunctionW for Unicode builds.

Since asio does not appear to use named events (always passes 0 for the event name), it doesn't matter which one it uses. On Windows, the -A functions are always wrappers for the -W functions, so it makes sense to use the wide-char variant (should save at least a jump.)

So I suggest that boost.asio should use CreateEventW consistently instead of CreateEvent.