Another fix for #254

This is to fix the same problem reported in #254; 
Even with the fix in #255, I'm still seeing this issue. I'm not using extraordinarily large lists of files, even. The total size of the incoming `pid_and_arguments` is only 1530 bytes in my case. 

I chose 2**16 to match what @andyl did in adc5766d

I don't see how it would affect this, but I'm using Ruby 2.0.0-p0; haven't tested on 1.9.