TW-1584: attr.{isnt,not} use partial matching

- Change attr.{isnt,not} to be the exact opposite of attr{:is,:},
  i.e. exact matching.
- Fix tests that assumed the old behavior was intended.

test/bug.906.t

@@ -66,7 +66,7 @@ unlike ($output, qr/two/,  "$ut: list - two included");
 
 $output = qx{../src/task rc:$rc list pro.not:a 2>&1};
 like   ($output, qr/zero/, "$ut: list - zero included");
-unlike ($output, qr/one/,  "$ut: list - one excluded");
+like   ($output, qr/one/,  "$ut: list - one included");
 unlike ($output, qr/two/,  "$ut: list - two excluded");
 
 $output = qx{../src/task rc:$rc list pro.not:a.b 2>&1};

test/filter-prefix.t

@@ -79,9 +79,9 @@ class TestFilterPrefix(TestCase):
     def test_list_project_not_foo(self):
         """Filter on not project name."""
         code, out, err = self.t(('list', 'project.not:foo'))
-        self.assertNotIn('one', out)
-        self.assertNotIn('two', out)
-        self.assertNotIn('three', out)
+        self.assertIn('one', out)
+        self.assertIn('two', out)
+        self.assertIn('three', out)
         self.assertIn('four', out)
         self.assertIn('five', out)
         self.assertIn('six', out)
@@ -112,18 +112,6 @@ class TestFilterPrefix(TestCase):
         self.assertIn('seven', out)
         self.assertIn('eight', out)
 
-    def test_list_project_not_ba(self):
-        """Filter on project partial non-match."""
-        code, out, err = self.t(('list', 'project.not:ba'))
-        self.assertIn('one', out)
-        self.assertIn('two', out)
-        self.assertIn('three', out)
-        self.assertNotIn('four', out)
-        self.assertNotIn('five', out)
-        self.assertNotIn('six', out)
-        self.assertNotIn('seven', out)
-        self.assertNotIn('eight', out)
-
     def test_list_description_has_foo(self):
         """Filter on description pattern."""
         code, out, err = self.t(('list', 'description.has:foo'))