Logging configuration with syslog-ng

I'd like to get my postgresql logging sent to the file
/var/log/postgresql.log, and have that file rotated  to
postgresql.log.0.gz etc.
my postgresql.conf says

log_destination = 'stderr,syslog'
syslog_facility = 'LOCAL0'
syslog_ident = 'postgres'

but the messages goes into /var/log/messages.
Does anyone knowhow to configure syslog-ng to do what I want?

my syslog-ng.conf file looks like this:

source src {
    unix-stream("/dev/log" max-connections(256));
    internal();
    file("/proc/kmsg");
};

destination messages { file("/var/log/messages"); };

log { source(src); destination(messages); };