Python: Add PEP-328 test example

Based on https://www.python.org/dev/peps/pep-0328/#guido-s-decision

Original "code" is in the Public Domain.

python/ql/test/experimental/dataflow/pep_328/__init__.py

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+pass

python/ql/test/experimental/dataflow/pep_328/package/__init__.py

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+bar = "bar"

python/ql/test/experimental/dataflow/pep_328/package/moduleA.py

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+foo = "foo"

python/ql/test/experimental/dataflow/pep_328/package/subpackage1/__init__.py

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+from .moduleY import spam
+from .moduleY import spam as ham
+from . import moduleY
+from ..subpackage1 import moduleY
+from ..subpackage2.moduleZ import eggs
+from ..moduleA import foo
+
+try:
+    from ...package import bar
+except Exception as e:
+    print(e)
+
+try:
+    from ...sys import path
+except Exception as e:
+    print(e)

python/ql/test/experimental/dataflow/pep_328/package/subpackage1/moduleX.py

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+from .moduleY import spam
+from .moduleY import spam as ham
+from . import moduleY
+from ..subpackage1 import moduleY
+from ..subpackage2.moduleZ import eggs
+from ..moduleA import foo
+
+try:
+    from ...package import bar
+except Exception as e:
+    print(e)
+
+try:
+    from ...sys import path
+except Exception as e:
+    print(e)

python/ql/test/experimental/dataflow/pep_328/package/subpackage1/moduleY.py

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+spam = "spam"

python/ql/test/experimental/dataflow/pep_328/package/subpackage2/__init__.py

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+pass

python/ql/test/experimental/dataflow/pep_328/package/subpackage2/moduleZ.py

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+eggs = "eggs"

python/ql/test/experimental/dataflow/pep_328/start.py

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+import package.subpackage1.moduleX