mktime takes localtime, or we skew the clocks

The following snippet shows that to create a proper timestamp, we should
feed mktime() with localtime() data rather than gmtime(), as it is locale
aware.

>>> from time import mktime, gmtime, localtime
>>> bad    = gmtime(mktime(gmtime()))
>>> good   = gmtime(mktime(localtime()))
>>> judge  = gmtime()
>>> if bad == good: "You're using UTC. Demonstration is impossible."
... elif bad == judge: "I can be wrong"
... elif good == judge: "but this shows I'm right"
...
"but this shows I'm right"

The above code checks whether gmtime() == gmtime(timestamp) from
mktime(). Obviously we don't get the same 'now' if we feed the bad value
to mktime.