[Compiler-sig] AST: jump offsets wrong when EXTENDED_ARG is used

[Neil Schemenauer]

The summary of the bug is that instrsize() is wrong inside
assemble_jump_offsets().  The instruction size depends on the length
of the jump and the length of jumps depend on instruction sizes.  I
think we need to iterate inside of assemble_jump_offsets().  We keep
iterating while instructions are gaining EXTENDED_ARGs.  Normally
iteration would not be required.

Does that sound correct?

  Neil