Use it to implement the behaviour where InternetReadFileExA does a 
synchronous request if the data is available and asynchronous otherwise.

wininet: Don't close the connection if the caller passes in zero for the number of bytes to be read.

Only close the connection when the bytes read equals the content length.

Fixup HTTP_DrainContent, which relied on the previous incorrect 
behaviour to instead close connections with no content length manually.

wininet: Fix basic authentication by putting Basic directing into the scheme field, as the pszAuthValue can have an optional realm string appended.

shell32/tests: With recent PSDKs, CSIDL_MYDOCUMENTS is a synonym for CSIDL_PERSONAL. So define our own constant.

In the PSDK HRESULT_FROM_WIN32() is now an inline function, and it is __HRESULT_FROM_WIN32() which is a macro.

user32/tests: SWP_STATECHANGED is an undocumented flag so define it ourselves. Fixes compilation with the PSDK.