use six privided functions/classes to support py2/py3 in one source. refs #1350.

tests/coverage.py

@@ -69,15 +69,11 @@ import sys
 import atexit
 import threading
 import token
-import types
 import zipimport
 from socket import gethostname
 
-# Python version compatibility
-try:
-    strclass = basestring   # new to 2.3
-except:
-    strclass = str
+import six
+
 
 # 2. IMPLEMENTATION
 #
@@ -845,7 +841,7 @@ class coverage:
         # On windows, the shell doesn't expand wildcards.  Do it here.
         globbed = []
         for morf in morfs:
-            if isinstance(morf, strclass):
+            if isinstance(morf, six.string_types):
                 globbed.extend(glob.glob(morf))
             else:
                 globbed.append(morf)