Better doc string detection

A bug in 2.7 test_descr.py revealed a problem with the way we were
detecting docstrings.

        __doc__ = DocDescr()

was getting confused with a docstring.

This program also reveals other bugs in 3.2+ but we'll deal with that
in another commit.

test/add-test.py

@@ -21,7 +21,7 @@ for path in py_source:
         cfile = "bytecode_%s%s/%s" % (version, suffix, short) + "c"
     print("byte-compiling %s to %s" % (path, cfile))
     optimize = 2
-    if vers >= (3, 0):
+    if vers > (3, 1):
         py_compile.compile(path, cfile, optimize=optimize)
     else:
         py_compile.compile(path, cfile)

test/simple_source/bug27+/03_doc_assign.py

@@ -0,0 +1,27 @@
+# From 2.7 test_descr.py
+# Testing __doc__ descriptor...
+# The bug in decompilation was erroneously matching
+# __doc__ = as a docstring
+
+"""This program is self-checking!"""
+
+def test_doc_descriptor():
+    # Testing __doc__ descriptor...
+    # Python SF bug 542984
+    class DocDescr(object):
+        def __get__(self, object, otype):
+            if object:
+                object = object.__class__.__name__ + ' instance'
+            if otype:
+                otype = otype.__name__
+            return 'object=%s; type=%s' % (object, otype)
+    class OldClass:
+        __doc__ = DocDescr()
+    class NewClass(object):
+        __doc__ = DocDescr()
+    assert OldClass.__doc__ == 'object=None; type=OldClass'
+    assert OldClass().__doc__ == 'object=OldClass instance; type=OldClass'
+    assert NewClass.__doc__ == 'object=None; type=NewClass'
+    assert NewClass().__doc__ == 'object=NewClass instance; type=NewClass'
+
+test_doc_descriptor()