Incorporate review comments courtesy of Neal Norwitz:

Incorporate review comments courtesy of Neal Norwitz:
* Perform the code length check earlier.
* Eliminate the extra PyMem_Free() upon hitting an EXTENDED_ARG.
* Assert that the NOP count used in jump retargeting matches the NOPs
  eliminated in the final step.
* Add an XXX note to indicate that more work is being to done to
  handle linenotab with intervals > 255.