final RETURN removal bug

We want to remove a final return from a module, but otherwise not.
Note we'll no lonager be able to verify functools.pyc as there
is now a return after a raise statement. That will have to be
delt with separately.

May address Issue #17.

test/simple_source/def/06_ifTrue_optimize_bug.py

@@ -0,0 +1,11 @@
+# Bug in uncompyle6 and pycdc for (some) Python 3 bytecodes.
+# Problem is JUMP_IF_FALSE is optimized away leaving
+# the unreachible LOAD_CONST below
+
+# Disassembly of lambda is:
+#  0       LOAD_CONST              2: 2
+#  3       RETURN_VALUE
+#  4       LOAD_CONST              3: 3
+#  7       RETURN_VALUE
+
+lambda: 2 if True else 3