Third-party libraries are stored here. Currently, Shapely is the only
one we're using which isn't available through package managers.

Shapely should be downloaded and extracted:

  wget http://pypi.python.org/packages/source/S/Shapely/Shapely-1.0.14.tar.gz
  tar -xvzf Shapely-1.0.14.tar.gz
  mv Shapely-1.0.14 Shapely
  rm Shapely-1.0.14.tar.gz
  
This will probably be handled by the makefile.