[PATCH] Suppress tr's stderr in the generate function

[Nicolai Dagestad]

This is a problemen with tr from the coreutils on arch, I don't know how it reacts on other
platforms.

tr started to complain about broken pipes recently.
It looks like it is because read closes the pipe when it has read enough characters.

After a little bit more testing, I found that when tr receives more than 4096 bytes of data 
and but less is read from the output pipe before it gets closed, I get the error message.
I assume this has something to do with the size of ome buffer that tr wants to write to it's 
stdout.
A patch could probably be send to tr to fix the behaviour, but I have to admit that I really
dislike GNU's coding style and would rather not have to understand their code...

Are there ever any important error messages from tr ?