Merge ast-branch to head

This change implements a new bytecode compiler, based on a
transformation of the parse tree to an abstract syntax defined in
Parser/Python.asdl.

The compiler implementation is not complete, but it is in stable
enough shape to run the entire test suite excepting two disabled
tests.
diff --git a/Misc/ACKS b/Misc/ACKS
index 58a2c86..b95902a 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -165,6 +165,7 @@
 Maxim Dzumanenko
 Hans Eckardt
 Grant Edwards
+John Ehresman
 Andrew Eland
 Lance Ellinghaus
 David Ely