Python: Add 2/3 specific query tests.

python/ql/test/2/query-tests/Variables/LeakyComp/LeakyComp.expected

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+| test.py:5:11:5:11 | x | x may have a different value in Python 3, as the $@ will not be in scope. | test.py:4:12:4:12 | x | list comprehension variable |
+| test.py:10:11:10:11 | y | y may have a different value in Python 3, as the $@ will not be in scope. | test.py:9:12:9:12 | y | list comprehension variable |

python/ql/test/2/query-tests/Variables/LeakyComp/LeakyComp.qlref

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+Variables/LeakingListComprehension.ql

python/ql/test/2/query-tests/Variables/LeakyComp/test.py

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+from __future__ import print_function
+
+def undefined_in_3():
+    [x for x in range(3)]
+    print(x)
+
+def different_in_3():
+    y = 10
+    [y for y in range(3)]
+    print(y)
+
+def ok():
+    [z for z in range(4)]
+
+#FP observed in sembuild
+def use_in_loop(seq):
+    [x for x in range(3)]
+    for x in seq:
+        use(x) #x redefined -- fine in 2 and 3.
+
+def test_6395(dev):
+    ret = {}
+
+    res = foo(dev)
+    if not res:
+        return False
+
+    for line in res.splitlines():  # pylint: disable=no-member
+        line = line.strip()
+        if not line:
+            continue
+
+        key, val = [val.strip() for val in bar(line)]
+        if not (key and val):
+            continue
+
+        mval = None
+        if ' ' in val:
+            rval, mval = [val.strip() for val in bar(val)]
+            mval = mval[1:-1]
+        else:
+            rval = val
+
+    return ret
+
+def test_6441(seq):
+    for var in seq:
+        foo(var)
+        [var for var in bar()]