Add test for a list comprehension that is nested in the left-hand part

of another list comp.  This caused crashes reported as SF bugs 409230
and 407800.

Note that the new tests are in a function so that the name lookup code
isn't affected by how many *other* list comprehensions are in the same
scope.

Lib/test/output/test_grammar

@@ -60,4 +60,5 @@ classdef
 [(1, 'Apple'), (1, 'Banana'), (1, 'Coconut'), (2, 'Apple'), (2, 'Banana'), (2, 'Coconut'), (3, 'Apple'), (3, 'Banana'), (3, 'Coconut'), (4, 'Apple'), (4, 'Banana'), (4, 'Coconut'), (5, 'Apple'), (5, 'Banana'), (5, 'Coconut')]
 [(1, 'Banana'), (1, 'Coconut'), (2, 'Banana'), (2, 'Coconut'), (3, 'Banana'), (3, 'Coconut'), (4, 'Banana'), (4, 'Coconut'), (5, 'Banana'), (5, 'Coconut')]
 [0, 0, 0]
+[[1, 2], [3, 4], [5, 6]]
 [('Boeing', 'Airliner'), ('Boeing', 'Engine'), ('Ford', 'Engine'), ('Macdonalds', 'Cheeseburger')]

Lib/test/test_grammar.py

@@ -661,6 +661,11 @@ def test_in_func(l):
 
 print test_in_func(nums)
 
+def test_nested_front():
+    print [[y for y in [x, x + 1]] for x in [1,3,5]]
+
+test_nested_front()
+
 check_syntax("[i, s for i in nums for s in strs]")
 check_syntax("[x if y]")