This is a rewrite of the block ordering code in the compiler package
(specifically, the flowgraph part). The previous code was littered with
self-admitted "hacks", "fixups" and "XXX" :-) They are all removed and
replaced with a clean ``order_blocks`` function which does the right
thing from the start.

The patch also replaces a wrong startBlock() with a nextBlock() in
compiler.pycodegen (startBlock can only be used when the previous block
does an unconditional transfer to another one, otherwise the two
adjacent blocks may not be emitted in order).

I've run test_compiler a couple of times, and tested execution of
several functions. They all run fine. Unless someone has specific
reasons to reject the patch, I'd recommend applying it even if not many
people use the compiler package :) I needed the fixes for my work on #2459.

By enabling TEST_ALL I've just run
``test_compiler.CompilerTest.testCompileLibrary`` against the whole
stdlib, and there were no errors. It's a good sign :-)

Neal, I don't have sufficient permissions to assign bugs to anybody, but
here you are in the nosy list. :)

Thanks Antoine.  For some reason I don't think I ever got an email about
this issue.  I did some further cleanups and optimizations.  Committed
as SVN rev 69373.

Lib/compiler is still in need of some fixing since it doesn't handle
decorators and some other new language features.  I'll try to keep at it.

> Thanks Antoine.  For some reason I don't think I ever got an email about
> this issue.  I did some further cleanups and optimizations.  Committed
> as SVN rev 69373.

Thanks! If I knew you hadn't received any notification I would have
tried to ping you... I'm glad this is finally accepted :)