If I am working in multiple branches on a single feature, I use git pull branch1 branch2 branch3 to pull all the changes into my master branch. However, all the commit logs of each branch are copied as well. How do I flatten the commit log down to a single message?
You can use interactive rebase and "squash" the commits -- see also the Git Ready Tutorial on squashing via rebase. Sorry to just dump a link on you but that's a pretty thorough tutorial. Oh, and this will also squash away your merges just fine.