#718 GetTickCount should be unsigned

[Julian O]

The call to win32api.GetTickCount() is returning a signed integer. It should be unsigned.

In particular, this causes problems when comparing it to, say, win32api.GetLastInputInfo() which returns an unsigned integer.

For more information, see this StackOverflow question: http://stackoverflow.com/questions/36312480/getlastinputinfo-and-gettickcount-are-not-consistent-with-each-other/