Ugly. A pile of new xxxFlags() functions, to communicate to the parser

that 'yield' is a keyword.  This doesn't help test_generators at all!  I
don't know why not.  These things do work now (and didn't before this
patch):

1. "from __future__ import generators" now works in a native shell.

2. Similarly "python -i xxx.py" now has generators enabled in the
   shell if xxx.py had them enabled.

3. This program (which was my doctest proxy) works fine:

from __future__ import generators

source = """\
def f():
    yield 1
"""

exec compile(source, "", "single") in globals()
print type(f())

1 files changed, 3 insertions, 0 deletions

diff --git a/Include/pythonrun.h b/Include/pythonrun.h
index 3877a82..6e9821b 100644
--- a/Include/pythonrun.h
+++ b/Include/pythonrun.h
@@ -45,6 +45,9 @@ DL_IMPORT(int) PyRun_InteractiveLoopFlags(FILE *, char *, PyCompilerFlags *);
 
 DL_IMPORT(struct _node *) PyParser_SimpleParseString(char *, int);
 DL_IMPORT(struct _node *) PyParser_SimpleParseFile(FILE *, char *, int);
+DL_IMPORT(struct _node *) PyParser_SimpleParseStringFlags(char *, int, int);
+DL_IMPORT(struct _node *) PyParser_SimpleParseFileFlags(FILE *, char *,
+							int, int);
 
 DL_IMPORT(PyObject *) PyRun_String(char *, int, PyObject *, PyObject *);
 DL_IMPORT(PyObject *) PyRun_File(FILE *, char *, int, PyObject *, PyObject *);