Org 8 support for shortcode sourcecode blocks

Hello, 

I made some changes that work (in R, at least) to support the WP SyntaxHighlighter Evolved plugin. This plugin does not expect pre-escaped HTML entities (e.g., \&lt;), so will not display code properly that contains them.  This change reverts those entities back to their original text, if the code is going to be displayed in a shortcode block. 

This removes the need to check for the org-version and call the protect/encode function on the text, also. 

I also added "r" to the list of supported languages, as the plugin contains a brush for R now. 

Thanks again!