git 1.7.4.6 required.

The following tests failed with git 1.7.2.1

* grit/test/test_commit.rb:201
* grit/test/test_repo.rb:422

The minimum version passing tests was 1.7.4.6

Environment:

* Ubuntu 10.04.03 LTS Desktop x86_64
* Compile git from source (github.com/git/git)