Modify git mergetool vimdiff's BAD UI(UI changes when git's BASE dosen't exist).
Always MERGED pain is bottom!
git clone https://github.com/haya14busa/git-mergetool-vimdiff-wrapper.git
cd git-mergetool-vimdiff-wrapper
cp myvimdiff /usr/local/bin/
git config --global mergetool.myvimdiff.cmd 'myvimdiff "$MERGED" "$LOCAL" "$BASE" "$REMOTE"'
git config --global merge.tool myvimdiff