[PL] Polish translations of rounded corners and drop shadow test 1 & 2

Hello Bert!

Here are another translations. This time, the small ones, but I've 
changed it a bit too. I add that by now all major browser should present 
box-shadow and border-radius correctly. So wrote it more like: in 2004 
this wasn't working, but now you shouldn't have any problems (but I left 
all original dates and mentions that those properties wasn't a standard).

-- 
Kindest regards,
Emil Sierżęga.