Combine the functionality of test_support.run_unittest()
and test_support.run_classtests() into run_unittest()
and use it wherever possible.

Also don't use "from test.test_support import ...", but
"from test import test_support" in a few spots.

From SF patch #662807.
diff --git a/Lib/test/test_StringIO.py b/Lib/test/test_StringIO.py
index 74bdf59..8c367e8 100644
--- a/Lib/test/test_StringIO.py
+++ b/Lib/test/test_StringIO.py
@@ -105,10 +105,12 @@
 
 
 def test_main():
-    test_support.run_unittest(TestStringIO)
-    test_support.run_unittest(TestcStringIO)
-    test_support.run_unittest(TestBufferStringIO)
-    test_support.run_unittest(TestBuffercStringIO)
+    test_support.run_unittest(
+        TestStringIO,
+        TestcStringIO,
+        TestBufferStringIO,
+        TestBuffercStringIO
+    )
 
 if __name__ == '__main__':
     test_main()