fixed issue #219

This is for fixing issue #219. This appears to work in my pip installation, but it might require adding an argument to setup.py or pip install when building for various distros, e.g.:

```
% python ./setup.py install --prefix=/opt/graphite --install-lib=/opt/graphite/lib
# or
% pip install --install-option='--prefix=/opt/graphite' --install-option='--install-lib=/opt/graphite/lib'
# etc.
```

I don't have Debian or Red Hat, so I haven't tested or attempted to update those build configurations.