Suggestion to centralize functional_asset_path

Hello, thanks for this great plugin.

I struggled for a short while to trace a lack of log data for sites within a Multisite install. Finally I tracked this back to the functional_asset_path() function using wp_upload_dir(). Hence a log file must be present in all blogs.dir/<blog_id>/files/nginx_helper/ for each sub-site to write to a log.

As this function is also used to retrieve the map.conf on sub-sites, this could also potentially be preventing proper cache clear on anything except the main site also.

Hence I modified 2 functions on my end for a smoother operation.

function functional_asset_path(){
	$dir = ABSPATH . 'wp-content/uploads';
	$path = $dir.'/nginx-helper/';
	return $path;
}

function functional_asset_url(){
	$dir = network_home_url() . '/wp-content/uploads';
	$url = $dir.'/nginx-helper/';
	return $url;
}

http://wordpress.org/extend/plugins/nginx-helper/