generate different activation scripts on MacOS and Linux

I'll remove this setting, because this seems to be specific to your machine: 
```
-DPYTHON_INCLUDE_DIR=/usr/local/Cellar/python/2.7.8/Frameworks/Python.framework/Headers 
-DPYTHON_LIBRARY=/usr/local/Cellar/python/2.7.8/Frameworks/Python.framework/Versions/2.7/lib/libpython2.7.dylib
```