vim: fix pre-Vim-8 plugin#packadd
vim: fix pre-Vim-8 plugin#packadd

Can't use "." as a delimiter because we'll get an unwanted split:

  foo.foo.vim -> foo, foo, vim
  foo::foo.vim -> foo, foo.vim

wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent