Test failure with boost 1.60

[uzadow]

libavg compiled using gcc 5.2 and boost 1.60 generates the following exception when importing libavg:

Traceback (most recent call last):
  File "./Test.py", line 97, in <module>
    import libavg
  File "/Users/uzadow/devel/libavg/libavg/src/test/libavg/__init__.py", line 13, in <module>
    from avg import *
TypeError: No registered converter was able to produce a C++ rvalue of type std::string from this Python object of type str

[uzadow]

Fixing in the bugfix/boost_1_60 branch