Check filetype setting when filename extension can't be used

[ggustafsson]

Would it be possible to make gist-vim check the filetype setting when the filename extension can't be used to figure out the type of file?

I often write shell scripts without a filename extension of .zsh and gist-vim assumes it's plain text, which is wrong. So plain text should only be assumed when there's no extension and &filetype is empty.

[mattn]

Gist service decide file type by file extension. But if user specify filename without file extension, gist-vim doesn't add file extension.

[mattn]

too many days are passed.