Please make it a warning if input directory is not found

[mb720]

Hi and thanks for your plugin!

I think it would save people a lot of debugging time if the plugin would log an explicit warning if the input directory for Less and CoffeeScript files is not found. It took me longer than I'm proud of that the reason why the webResourceCompileLess task was being skipped, is that the plugin was looking in a different directory than I expected.

This could have been avoided if the plugin would warn users if the input directory does not exist instead of logging an info message as it currently does.

Thanks again for your plugin!