Make str/str8 comparisons return True/False for !=/==.

Code that has been returning str8 becomes much more apparent thanks to this
(e.g., struct module returning str8 for all string-related formats or sqlite3
passing in str8 instances when converting objects that had a __conform__
method).  One also has to watch out in C code when making a key from char *
using PyString in the C code but a str instance in Python code as that will not
longer compare equal.

Once str8 gains a constructor like the current bytes type then
test_modulefinder needs a cleanup as the fix is a little messy in that file.

Thanks goes to Thomas Lee for writing the patch for the change giving an
initial run-down of why most of the tests were failing.
diff --git a/Lib/test/test_subprocess.py b/Lib/test/test_subprocess.py
index 3c92675..fea98dc 100644
--- a/Lib/test/test_subprocess.py
+++ b/Lib/test/test_subprocess.py
@@ -24,7 +24,7 @@
 # shutdown time.  That frustrates tests trying to check stderr produced
 # from a spawned Python process.
 def remove_stderr_debug_decorations(stderr):
-    return re.sub(r"\[\d+ refs\]\r?\n?$", "", str8(stderr))
+    return re.sub(r"\[\d+ refs\]\r?\n?$", "", str(stderr))
 
 class ProcessTestCase(unittest.TestCase):
     def setUp(self):