I don't know if you've been following topic "A lot of mods for RC 0.1 - stable ..." @ http://roundcubeforum.net/forum/index.php?topic=2562.0 (http://roundcubeforum.net/forum/index.php?topic=2562.0), but there seem to be some nice additions for roundcube by rosali. Any chance of them being incorporated in the svn tree sometime soon?
Try to post a feature request in the trac (trac.roundcube.net).
You can't just merge other peoples code into the SVN... it doesn't work like that. the code must be audited - there is nothing to say that the code changes he made don't introduce tons of bugs and security vulnerabilities.
However, as RC is GPL, whoever made the code "enhancements" is welcome to start their own project and release it under GPL.