Apple Removed Roundcube because within recent months, Roundcube moved to GPL license 3.0 which means it can't be bundled in commericial software.
You can install Roundcube 0.7.2 .
Note Roundcube 0.8 stable will be available soon since they have a few bugs left to work out. And it's a nice big facelift change to the new Larry theme.
Note you might want to install mysql server vs using postgresql since some carddav plug-ins use mysql.
Can I presume you followed the install instructions and installed mysql and then created the user that is needed in order to connect? Did you also fill the database with the sql script that they supply using the new user you created in the database?
I also had to edit the main config file to set the imap url to use tls://localhost for its connection -
// %d - domain (http hostname without the first part)
// %s - domain name after the '@' from e-mail address provided at login screen
// For example %n = mail.domain.tld, %d = domain.tld
$rcmail_config['default_host'] = 'ssl://localhost';
// TCP port used for IMAP connections
$rcmail_config['default_port'] = 993;
// IMAP AUTH type (DIGEST-MD5, CRAM-MD5, LOGIN, PLAIN or empty to use
// best server supported one)
$rcmail_config['imap_auth_type'] = 'LOGIN';
Also notice the port number and ath type lines.