Untitled

git fetch mootools
git checkout mootools/master
git branch -m master mess
git checkout -b master
git checkout mess
git rebase -i master

squash it all..

git checkout -b vendor-prefix
git checkout mootools/master Source/Element.Event.js
git checkout mootools/master package.yml
git commit -am "Resetting to mootools/master"

git checkout mess
git branch -m mess event-change
git rm Source/Browser/Browser.Styles.js
git checkout mootools/master Source/Element/Element.Style.js
git checkout mootools/master package.yml
git commit -am "Resetting to mootools/master"

git push origin vendor-prefix
git push origin event-change

go to github and close the old pull request.
go to your mootools-core repo. select the vendor-prefix branch (or http://github.com/csuwldcat/mootools-core/tree/vendor-prefix)
do a pull request. verify that you didn't bring a long any unwanted cruff.
repeat for event-change.