Install from the tarball for the latest stable version.
Sorry, but a developer just made a change to the Roundcube installer this month, so its not in a stable release yet.
Apparently its an attempt to fix a problem where the timestamps in the Roundcube log files are not the same timezone format as those of the Apache server.
Currently DreamHost doesn't specify a timezone for date.timezone in the PHP.INI file deployed on its servers. The Roundcube installer was changed to make it a deal breaker if there is no timezone specified there. AFAIK only the installer actually needs a value specified for date.timezone too.
If a version is released with this change still in it then no one will be able to install Roundcube at DreamHost without working around it. Workarounds would involve adding a call to ini_set('date.timezone', 'America/Los_Angeles') to the installer script or using a custom PHP.INI file that sets date.timezone, or commenting out the check altogether.
The discussion about this change is at http://lists.roundcube.net/ on the devs list under 'Different Timezone offsets in my RoundCube log' It doesn't seem like this change was thought through before it was made, or at least there is no discussion of the consequences.
It seems the real bug is that the function that writes the log file entry doesn't specify the timezone when obtaining the date string. And of course this change didn't fix that bug, and the guy that needs the log file problem fixed has said so but who knows if the change will be backed out?
Filed Ticket #1485989 - installer checks date.timezone for no reason
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