Fixed random_element() for rational quaternionic fractional ideals

Added QuaternionFractionalIdeal_rational.random_element() to overwrite the ideal.random_element()-method, which doesn't work for fractional ideals.

src/sage/algebras/quatalg/quaternion_algebra.py

@@ -2294,6 +2294,20 @@ def __repr__(self):
             'Fractional ideal (2 + 6*j + 4*k, 2*i + 4*j + 2*k, 8*j, 8*k)'
         """
         return 'Fractional ideal %s' % (self.gens(),)
+
+    def random_element(self, *args, **kwds):
+        """
+        Return a random element in the rational fractional ideal ``self``.
+
+        EXAMPLES::
+
+            sage: B.<i,j,k> = QuaternionAlgebra(211)
+            sage: I = B.ideal([1, 1/4*j, 20*(i+k), 2/3*i])
+            sage: x = I.random_element()  # random
+            sage: x in I
+            True
+        """
+        return sum(ZZ.random_element(*args, **kwds) * g for g in self.gens())
 
     def quaternion_order(self):
         """