If I ls-tree a certain tree and get a list of blobs and trees, how can I discover the last commit related to those blobs and trees? I'm looking for something like this: 
$ git ls-tree HEAD
...
100644 blob  734713bc047d87bf7eac9674765ae793478c50d3   myfile
...
$ git show --commit 734713bc047d87bf7eac9674765ae793478c50d3
commit 734713bc047d87bf7eac9674765ae793478c50d3
Author: Scott Chacon <schacon@gmail.com>
Date:   Fri Jan 2 18:32:33 2009 -0800
    fixed refs handling, added gc auto, updated tests