add test for issue #148: EINVAL is randomly raised on Mac OS X. Thanks to Mark Hingston.

greentest/test__subprocess.py

 # mostly tests from test_subprocess.py that used to have problems
 import sys
 import os
+import errno
 import greentest
 from gevent import subprocess
 
@@ -117,6 +118,16 @@ class Test(greentest.TestCase):
             if p.poll() is None:
                 p.send_signal(9)
 
+    def test_issue148(self):
+        for i in range(7):
+            try:
+                p1 = subprocess.Popen('this_name_must_not_exist')
+            except OSError as ex:
+                if ex.errno != errno.ENOENT:
+                    raise
+            else:
+                raise AssertionError('must fail with ENOENT')
+
 
 if __name__ == '__main__':
     greentest.main()