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.

Include/ast.h

@@ -0,0 +1,13 @@
+#ifndef Py_AST_H
+#define Py_AST_H
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+extern DL_IMPORT(mod_ty) PyAST_FromNode(const node *, PyCompilerFlags *flags,
+					const char *);
+
+#ifdef __cplusplus
+}
+#endif
+#endif /* !Py_AST_H */