Import setuptools if it's available.

setup.py

@@ -16,6 +16,12 @@
 
 import distutils.core
 import sys
+# Importing setuptools adds some features like "setup.py develop", but
+# it's optional so swallow the error if it's not there.
+try:
+    import setuptools
+except ImportError:
+    pass
 
 # Build the epoll extension for Linux systems with Python < 2.6
 extensions = []