How to figure out which, if any, update changed /etc/localtime from a link to a hard file?

[David M. Karr]

So, I had recently discovered a bug with Java not using the correct date 
ranges for DST.  What I've determined is that Java requires 
/etc/localtime to be a symlink, not a hard file.  When I replaced the 
hard file with a link to the correct file, it fixed my problem.

Now, what I'd like to find out is how and when /etc/localtime became a 
hard file.

I have no idea whether the original Ubuntu 8.10 installation was in this 
state or not.  It could have happened when I installed one of the many 
updates that come through.

is there any way to search through the list of updates that I've 
installed to see whether any of them would have done this?