This could cause problems on very unstable connections. When next()
wasn't called for a long time, and then it was called very frequently
(so time() returned 4x the same value) we were clean()ing the
window.dequeue so much so we got "last" equal to "deque[0][0]",
therefore counter/(last - deque[0][0]) could cause a division by zero.
In theory, this would also solve some temporary situations when
subsequent calls to time() did not return consecutive values:
>>> a = time() ; b = time() ; a > b
True
Resolves: rhbz#2103093
Version: 1.6-4
