While my system was performing a
$ brew update && brew upgrade we had a power failure and my iMac shut down while updating packages/dependancies.
After rebooting I tried to run
$ brew update && brew upgrade again and encountered the following error:
fatal: unable to access 'https://github.com/mxcl/homebrew/': transfer closed with outstanding read data remaining
Error: Failure while executing: git pull -q origin refs/heads/master:refs/remotes/origin/master
$ brew doctor strangely returns a clean bill of health.