[pypy-dev] Refactored flow model

[Armin Rigo]

Hello everybody,

A bunch of commits from yesterday: Holger and I rewrote the classes that we
use to represent control flow graphs.  We had agreed during the whole Berlin
sprint that the many XxxBranch classes weren't very practical to use, and we
discussed an alternative at the end of the sprint.  That's what we just
implemented.

There is also a much nicer dot-generator now.  The graphs are becoming quite
comprehensible now, much shorter, with nice colors, and all :-)
Try running the tests with '-v' (either individual tests or the test_all.py
script); if you installed dot, it will leave Postscript files in
/tmp/usession-*/*.ps, with both the non-simplified and the simplified graph
showing on the same page.


A bientot,

Armin.