ultimate-vim/sources_non_forked/vim-markdown/ftdetect/markdown.vim

" markdown filetype file
au BufRead,BufNewFile *.{md,mdown,mkd,mkdn,markdown,mdwn} set filetype=markdown
au BufRead,BufNewFile *.{md,mdown,mkd,mkdn,markdown,mdwn}.{des3,des,bf,bfa,aes,idea,cast,rc2,rc4,rc5,desx} set filetype=markdown