Fix some unicode issues with logging

[jcftang]

I was seeing hanging behaviour. When I have this patch my builds succeed.

[ruslo]

I've seen some problems with encoding before but it was error from Python, not hanging:

• Non UTF8 console encoding #62

I'm not sure I understand all parts, can you please explain in details what is happening? I guess leaving comments with link to documentation would be nice.

[jcftang]

My build process generates output which causes this to occur...

Exception in thread Thread-6:
Traceback (most recent call last):
  File "/usr/lib64/python3.4/threading.py", line 911, in _bootstrap_inner
    self.run()
  File "/usr/lib64/python3.4/threading.py", line 859, in run
    self._target(*self._args, **self._kwargs)
  File "/home/build/polly/bin/detail/call.py", line 41, in fanout
    log_file.write(s)
UnicodeEncodeError: 'ascii' codec can't encode character '\xf6' in position 75: ordinal not in range(128)

AFAIK the build process for the project that I am working has many different languages which get emitted by whatever compiler/preprocessor that I am using. This output causes a crash in one of the threads that polly.py spawns and it then causes the script to just wait and never succeed.

[ruslo]

Please try fix from #141

[jcftang]

FYI the patch looks good to me, will test later.