No appropriate QA test for gr::prefs / config file parser

[mbr0wn]

There's no QA for gr::prefs at all.

Being core functionality, http://gnuradio.org/redmine/issues/918 will have to wait until I implement one.

[marcusmueller]

There's no QA for gr::prefs at all.

Not true:

    def test_001(self):
        p = gr.prefs()

        # Read some options
        self.assertFalse(p.has_option('doesnt', 'exist'))

        # At the time these tests are run, there is not necessarily a default
        # configuration on the build system, so not much to do with testing here

But truth be told, that is not sufficient testing.

[marcusmueller]

This being a really well-stressed multi-platform-problematic core component, lack of testing does constitute a bug, since we'll not notice failures.

There's been at least one acute instance of this biting us (namely, 3.7 < 3.7.13 can't change audio settings since the prefs file handling was broken).

[marcusmueller]

remains valid, should be sensibly fixable, long-term maintainability issue.