Fixed wx.Timer to not need to hold an extra reference to itself, so it

Fixed wx.Timer to not need to hold an extra reference to itself, so it
can be cleaned up properly when the Python reference to it is
released.  Also fixed wx.FutureCall so that its timer can be
restarted.  Souped up the Timer demo to show and explain the various
ways to use a wx.Timer.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@26033 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775