A package corresponding to TIP 245 that gives you the amount of time a user has been inactive.

I packaged up the code I found in the TIP proposal patch and have put it at http://www.dedasys.com/freesoftware/files/ (look for tkinactive).  It's in an initial "it works for me" state, but could probably use more fixing, and could certainly use someone with MacOS X expertise to add that bit back in (I don't have a Mac system to test to do the work on).