Description: Don't cythonize in the clean target.
 Changes the source tree when it shouldn't.
Author: Bas Couwenberg <sebastic@debian.org>

--- a/setup.py
+++ b/setup.py
@@ -91,7 +91,7 @@ else:
 
 
 # use Cython to generate the C code (_proj.c) from _proj.pyx
-if USE_CYTHON:
+if USE_CYTHON and "clean" not in sys.argv:
     try:
         from Cython.Build import cythonize
     except ImportError: