Do not pull from master when updating

[jaimeMF]

If linuxbrew is going to be the main branch, when calling brew upgrade it should checkout linuxbrew and the pull from refs/remotes/origin/linuxbrew. Otherwise it merges the changes from the master branch.

[sjackman]

As a quick hack, the following will work:
sed -i 's/\bhomebrew\b/linuxbrew/g;s/\bmxcl\b/homebrew/g;s/\borigin\b/linuxbrew/g;s/\bmaster\b/linuxbrew/g' Library/Homebrew/cmd/update.rb

Unfortunately, it breaks taps, which still need to pull the branch master rather than linuxbrew.

[jaimeMF]

Thanks