git-pull-branch script

I've attached the 1-line git-pull-branch script that I just whipped 
together, in case anybody finds it useful.

On occasion, I need to pull one branch into another branch, inside the 
same repo.  For this case, the objects are already present, so we can 
skip the git-fetch-script step of git-pull-script completely.  I also 
modify the commit message so that we log the fact that we pulled a branch.