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.

Lib/test/test_doctest.py

@@ -1559,11 +1559,11 @@ Run the debugger on the docstring, and then restore sys.stdin.
 
     >>> try: doctest.debug_src(s)
     ... finally: sys.stdin = real_stdin
-    > <string>(1)?()
+    > <string>(1)<module>()
     (Pdb) next
     12
     --Return--
-    > <string>(1)?()->None
+    > <string>(1)<module>()->None
     (Pdb) print x
     12
     (Pdb) continue
@@ -1601,7 +1601,7 @@ def test_pdb_set_trace():
       >>> try: runner.run(test)
       ... finally: sys.stdin = real_stdin
       --Return--
-      > <doctest foo[1]>(1)?()->None
+      > <doctest foo[1]>(1)<module>()->None
       -> import pdb; pdb.set_trace()
       (Pdb) print x
       42
@@ -1637,7 +1637,7 @@ def test_pdb_set_trace():
       (Pdb) print y
       2
       (Pdb) up
-      > <doctest foo[1]>(1)?()
+      > <doctest foo[1]>(1)<module>()
       -> calls_set_trace()
       (Pdb) print x
       1
@@ -1686,7 +1686,7 @@ def test_pdb_set_trace():
       [EOF]
       (Pdb) next
       --Return--
-      > <doctest foo[2]>(1)?()->None
+      > <doctest foo[2]>(1)<module>()->None
       -> f(3)
       (Pdb) list
         1  -> f(3)
@@ -1779,7 +1779,7 @@ def test_pdb_set_trace_nested():
     (Pdb) print y
     1
     (Pdb) up
-    > <doctest foo[1]>(1)?()
+    > <doctest foo[1]>(1)<module>()
     -> calls_set_trace()
     (Pdb) print foo
     *** NameError: name 'foo' is not defined