filetypes are not split when using lazy loading.

basically the following works:
```
Plug 'mattn/emmet-vim', { 'for': [ 'jinja.html', 'html', 'mustache', 'jinja' ] }
```

but just `jinja` or just `html` does not:
```
Plug 'mattn/emmet-vim', { 'for': [ 'html', 'mustache', 'jinja' ] }
```
I am happy to leave `jinja.html` in my config, but based on [this help](https://vi.stackexchange.com/a/4941) it seems that it should take into consideration either.

```
latest
```

- Type:
- [X] Bug
- [X] Enhancement
- [X] Feature Request
- [ ] Question
- OS:
- [ ] All/Other
- [X] Linux
- [ ] OS X
- [ ] Windows
- Vim:
- [X] Terminal Vim
- [ ] GVim
- [ ] Neovim