vimfiler can't close an existing vimfiler when the vimfiler buffer has multiple filetypes.

vimfiler can't close a window correctly when the window has multiple filetypes. For example, `&filetype` is `project.vimfiler`. The root cause is that `vimfiler#util#get_vimfiler_winnr` can't return winnr if a buffer has multiple filetypes(because get_vimfiler_winnr compares filetypes using `==#` on closing a vimfiler window.). I think that comparing filetypes with regexp fixes this issue.