Add support for django-plus.vim

[tweekmonster]

Hi! I created a plugin called django-plus.vim and would like UltiSnips to work with it since Django is an exceptional case in Vim.

The django filetype is considered a text template in Vim. But, for users to easily enable the Django snippets in Python scripts, the python.django filetype can be used. This causes some problems since plugins might not consider the dotted filetype, and filetypes like markdown.django or yaml.django (or even python.django) should actually be including htmldjango.snippets.

The other problem is that using :UltisnipsEdit without arguments, one would expect django.snippets to be loaded, but python.snippets is loaded instead. The filetype would need to be django.python, but will break syntax highlighting in Python scripts.

django-plus.vim reliably detects files in a Django project and sets b:is_django and leaves the filetype alone. I attempted to manually call UltiSnips#FileTypeChanged() and UltiSnipsAddFiletypes django in an after/ftplugin scripts, but that isn't reliable since other plugins can re-set filetype.

This shouldn't affect anyone who doesn't have django-plus.vim installed. If there's a better way to do this, let me know.

[seletskiy]

@tweekmonster: I doubt that UltiSnips should have any 3-rd party plugin code.

Did you tried to register autocmd FileType * <your-code-that-register-filetype-in-ultisnips>?

[tweekmonster]

I doubt that UltiSnips should have any 3-rd party plugin code.

I don't disagree with you. I think I took the wrong approach because it was late. It might be better if UltiSnips#FileTypeChanged() allowed the filetype to be passed in instead.

I updated the PR. If you think that's reasonable, you can change the PR title to match the commit message so it makes sense.

[seletskiy]

@tweekmonster: Yep, that's much more reasonable! Thanks!

[tweekmonster]

Thanks!