Ensure debug logging is unbuffered on Windows

Since Windows does not support line-buffering we should use unbuffered
output.  This ensures that debug output is visible immediately rather
than held in a buffer for an unspecified amount of time.

The alternative workaround is to sprinkle fflush(3) calls everywhere.
It's more efficient but ugly.

Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>
Fix QSysInfo::WordSize type size_t -> int

Since QSysInfo::WordSize is an enum the type is int.

Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>
Move NJClient::Disconnect() m_downloads.Empty()

Clearing m_downloads requires first deleting each RemoteDownload and
then emptying the list itself.  Make these two steps adjacent in the
source code to eliminate the risk of accessing a freed RemoteDownload
before m_downloads.Empty() is called.

Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>