Rename libfuturize/tests to libfuturize/test_scripts.

* They aren't really tests -- merely grist for the test mill.
Remove empty directory libfuturize.tests from setup.py packages list

Otherwise "python setup.py build" bails with this message:

    error: package directory 'libfuturize/tests' does not exist
Add note about v0.3.5 to NEWS.txt