set .di files as "d" filetype

vimrc

@@ -102,6 +102,7 @@ if has("autocmd")
     autocmd FileType text setlocal textwidth=78
     autocmd BufRead,BufNewFile *.icf set syntax=cpp
     autocmd FileType ruby setlocal sw=2 ts=2 sts=2
+    autocmd BufRead,BufNewFile *.di set filetype=d
 
     " When editing a file, always jump to the last known cursor position.
     " Don't do it when the position is invalid or when inside an event handler