broken header

pype dies with a broken pipe error if subsequent pipe breaks the stream (e.g. `head`):

```
Traceback (most recent call last):
  File "/home/jgeyti/bin/pype", line 373, in <module>
    pype(sys.stdin)
  File "<string>", line 7, in pype
IOError: [Errno 32] Broken pipe
close failed in file object destructor:
Error in sys.excepthook:

Original exception was:
```
