Added simple implementation to check if git is installed before
executing commands.
Tightened up git checking to check for a minimum installed version of
Git.
Added tests for a minimumGit version of 1.8.0.
Changed name of git check method to be more descriptive.
Fix to make tests pass in Ruby 1.9.3
Merge pull request #127 from JCook21/CheckGit

In lieu of other comments I'm going to go ahead and merge this.