Fixed post_action to not trigger "header already sent" alert. The alert was introduced in 03ff14058272 (1.5.4), and was triggered on each post_action invocation. There is no real need to call header filters in case of post_action, so return NGX_OK from ngx_http_send_header() if r->post_action is set.

au BufRead,BufNewFile *.nginx set ft=nginx
au BufRead,BufNewFile */etc/nginx/* set ft=nginx
au BufRead,BufNewFile */usr/local/nginx/conf/* set ft=nginx
au BufRead,BufNewFile nginx.conf set ft=nginx