Added support for translators in Yelp

[Mikael Hallendal <micke codefactory se>]

Hi!

I did another string-change in Yelp (sorry!) but I think you guys will
like this one :)

I found that in gnome-calculator they did a cool thing. They added a
string for translation called translator_credits, translators add there
name here in the po-file and they will be included in the about-box.

Is this the correct way of doing this? If it is, just start adding your
names, otherwise, let me know how it should be done.

Regards and thanks a million for all the great work you all put in!
  Mikael Hallendal

-- 
Mikael Hallendal                micke@codefactory.se
CodeFactory AB                  http://www.codefactory.se/
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