Require GEOS to be preinstalled.
Require GEOS to be preinstalled.

New custom install command fails if we can't locate a GEOS
shared library (using same method as in shapely/geos.py).

Closes #218.

mindw/shapely,abali96/Shapely,mindw/shapely,jdmcbr/Shapely,mouadino/Shapely,abali96/Shapely,jdmcbr/Shapely,mouadino/Shapely