add support for rsyslog v2 clients

add support for old clients using rsyslog v2. Like RedHat 5.4 and earlier or Suse 10.


It replace https://github.com/ghoneycutt/puppet-module-rsyslog/pull/44 where GH said:
instead of two templates for the same file, there should be conditional logic within the template.
Also, could you do a validate_re() on $rsyslog_conf_version to ensure it is '2' or '3'.
Oh yea, would also add a note about this to the Compatibility section of the README.