Syntax highlighting for git commit messages, config files, etc. is
included with the vim distribution as of vim 7.2, and should work
automatically.

If you have an older version of vim, you can get the latest syntax
files from the vim project:

  http://vim.svn.sourceforge.net/viewvc/vim/trunk/runtime/syntax/git.vim
  http://vim.svn.sourceforge.net/viewvc/vim/trunk/runtime/syntax/gitcommit.vim
  http://vim.svn.sourceforge.net/viewvc/vim/trunk/runtime/syntax/gitconfig.vim
  http://vim.svn.sourceforge.net/viewvc/vim/trunk/runtime/syntax/gitrebase.vim
  http://vim.svn.sourceforge.net/viewvc/vim/trunk/runtime/syntax/gitsendemail.vim

To install:

  1. Copy these files to vim's syntax directory $HOME/.vim/syntax
  2. To auto-detect the editing of various git-related filetypes:
	$ cat >>$HOME/.vim/filetype.vim <<'EOF'
	autocmd BufNewFile,BufRead *.git/COMMIT_EDITMSG    setf gitcommit
	autocmd BufNewFile,BufRead *.git/config,.gitconfig setf gitconfig
	autocmd BufNewFile,BufRead git-rebase-todo         setf gitrebase
	autocmd BufNewFile,BufRead .msg.[0-9]*
		\ if getline(1) =~ '^From.*# This line is ignored.$' |
		\   setf gitsendemail |
		\ endif
	autocmd BufNewFile,BufRead *.git/**
		\ if getline(1) =~ '^\x\{40\}\>\|^ref: ' |
		\   setf git |
		\ endif
	EOF