I had a quick look at it.
The first problem I had was the example needed to be in it's own folder.
The file test_pstring.pde in examples should be in a sub folder called test_pstring
That didn't make it work. I had a read of Arduino 1.0 is Out: Here's What You Need To Know - Make:
They say, "New functionality has been added to Streams (the underlying class that anything that uses .print() statements), Ethernet, Wire (I2C), and low level input/output."
So now I get the same error.
Looks like you will have to go back to 0.22 or find another way to do your printing