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.