Check hygene before importing site or installing distribute.

dev.py

@@ -26,13 +26,26 @@ for d in 'eggs', 'develop-eggs', 'bin', 'parts':
 if os.path.isdir('build'):
     shutil.rmtree('build')
 
+nosite = 'site' not in sys.modules
+
+######################################################################
+# Make sure we have a relatively clean environment
+try:
+    import pkg_resources, setuptools
+except ImportError:
+    pass
+else:
+    raise SystemError(
+        "Buildout development with a pre-installed setuptools or "
+        "distribute is not supported.%s"
+        % ('' if nosite else ' Try running with -S option to Python.'))
+
 ######################################################################
 # handle -S
 
 def normpath(p):
     return p[:-1] if p.endswith(os.path.sep) else p
 
-nosite = 'site' not in sys.modules
 if nosite:
     # They've asked not to import site.  Cool, but distribute is going to
     # import it anyway, so we're going to have to clean up. :(
@@ -42,18 +55,6 @@ if nosite:
 else:
     to_remove = ()
 
-######################################################################
-# Make sure we have a relatively clean environment
-try:
-    import pkg_resources, setuptools
-except ImportError:
-    pass
-else:
-    raise SystemError(
-        "Buildout development with a pre-installed setuptools or "
-        "distribute is not supported.%s"
-        % ('' if nosite else ' Try running with -S option to Python.'))
-
 ######################################################################
 # Install distribute
 ez = {}