extract real comments

The comment extraction functions provided by ast_c return all tokens between the code elements and not just the ones that are actual comments. The non comment tokens were being filtered out in the conversion to script variables, but only for the string representations, not for the internal representations. Change the metavariable binding so that it only contains information about real comments. Note that the code making the script bindings does not change, because it is still necessary to extract the strings from their token data structures.