allow custom runtime params on freebsd

[sethlyons]

this is a continuation of #79 and incorporates some of the changes from #73.

@olevole was there really not a better way to incorporate $logfile than to redirect to it? that seems really ugly.

[olevole]

@sethlyons AFAIK, when i wrote my version, i just take this part from Windows or Linux template:

https://github.com/saz/puppet-memcached/blob/master/templates/memcached_windows.erb#L29

in those times in memcached was not able to specify logfile (it seems now nothing has changed). But now i see in Linux tamplate used pipe end redirect to logger ;-)

https://github.com/saz/puppet-memcached/blob/master/templates/memcached_sysconfig.erb#L28

May be it better solution for FreeBSD too.

[saz]

I'll merge this PR now.
If any of you know a better way of the log handling part, please send in a new PR.

Thanks to all of you!

[olevole]

Great! Finally I can remove my fork for FreeBSD-users now ;-)