Tweak test for random ImportWarning from Python 3: ImportWarning: can't...

Tweak test for random ImportWarning from Python 3: ImportWarning: can't resolve package from __spec__ or __package__, falling back on __name__ and __path__

src/greentest/test__subprocess_interrupted.py

 import sys
-from _six import xrange
-
 
 if 'runtestcase' in sys.argv[1:]:
     import gevent
     import gevent.subprocess
     gevent.spawn(sys.exit, 'bye')
-    gevent.subprocess.Popen('python -c "1/0"'.split())
+    # Look closely, this doesn't actually do anything, that's a string
+    # not a division
+    gevent.subprocess.Popen([sys.executable, '-c', '"1/0"'])
     gevent.sleep(1)
 else:
     import subprocess
-    for _ in xrange(5):
-        out, err = subprocess.Popen([sys.executable, __file__, 'runtestcase'], stderr=subprocess.PIPE).communicate()
-        if b'refs' in err:
+    for _ in range(5):
+        out, err = subprocess.Popen([sys.executable, '-W', 'ignore',
+                                     __file__, 'runtestcase'],
+                                    stderr=subprocess.PIPE).communicate()
+        if b'refs' in err: # Something to do with debug mode python builds?
             assert err.startswith(b'bye'), repr(err)
         else:
             assert err.strip() == b'bye', repr(err)