Fix Py3 incompatible in tests.

test/operands.py

@@ -3,7 +3,11 @@
 # Tests accessing of instruction operands.
 
 from llvm.core import *
+try:
     from StringIO import StringIO
+except ImportError:
+    from io import StringIO
+
 import logging, unittest
 
 m = None

test/passes.py

@@ -3,8 +3,11 @@
 from llvm.core import *
 from llvm.passes import *
 from llvm.ee import *
-
+try:
     from StringIO import StringIO
+except ImportError:
+    from io import StringIO
+
 
 import logging, unittest
 

test/testattrs.py

@@ -1,8 +1,12 @@
 #!/usr/bin/env python
 
 from llvm.core import *
+try:
+    from StringIO import StringIO
+except ImportError:
     from io import StringIO
 
+
 import unittest
 
 def make_module():