Applied correct commits of master branch.

TODO

@@ -84,8 +84,3 @@ smvv@multivac ~/work/trs $ printf "0/1\n??" | ./main.py
 <Possibility root="0 / 1" handler=divide_numerics args=(0, 1)>
 Division of 0 by 1 reduces to 0.
 Division of 0 by 1 reduces to 0.
-
- - Should powers have a higher precedence thatn negation while printing?
-   the current situation: -(x ^ 2) and -x ^ 2 (the latter instead of (-x) ^ 2)
-   might be desired: -x ^ 2 instead of -(x ^ 2), and explicit parentheses for
-   (-x) ^ 2

tests/test_leiden_oefenopgave_v12.py

@@ -34,5 +34,3 @@ class TestLeidenOefenopgaveV12(TestCase):
             '-72x ^ 3 + 96x ^ 2 - x * 32',
             '-72x ^ 3 + 96x ^ 2 + 32 * -x',
             '-72x ^ 3 + 96x ^ 2 - 32x'])
-            # TODO: Should powers have a higher precedence than negation
-            #       while printing?

tests/test_rules_goniometry.py

@@ -13,5 +13,4 @@ class TestRulesGoniometry(RulesTestCase):
 
     def test_add_quadrants(self):
         return
-        root = tree('sin(x) ^ 2 + cos(x) ^ 2')
-        self.assertEqual(add_quadrants(root, ()), 1)
+        self.assertEqual(add_quadrants(None, ()), 1)