PEP 227 implementation

The majority of the changes are in the compiler.  The mainloop changes
primarily to implement the new opcodes and to pass a function's
closure to eval_code2().  Frames and functions got new slots to hold
the closure.

Include/compile.h
    Add co_freevars and co_cellvars slots to code objects.
    Update PyCode_New() to take freevars and cellvars as arguments
Include/funcobject.h
    Add func_closure slot to function objects.
    Add GetClosure()/SetClosure() functions (and corresponding
    macros) for getting at the closure.
Include/frameobject.h
    PyFrame_New() now takes a closure.
Include/opcode.h
    Add four new opcodes: MAKE_CLOSURE, LOAD_CLOSURE, LOAD_DEREF,
    STORE_DEREF.
    Remove comment about old requirement for opcodes to fit in 7
    bits.
compile.c
    Implement changes to code objects for co_freevars and co_cellvars.

    Modify symbol table to use st_cur_name (string object for the name
    of the current scope) and st_cur_children (list of nested blocks).
    Also define st_nested, which might more properly be called
    st_cur_nested.  Add several DEF_XXX flags to track def-use
    information for free variables.

    New or modified functions of note:
    com_make_closure(struct compiling *, PyCodeObject *)
        Emit LOAD_CLOSURE opcodes as needed to pass cells for free
        variables into nested scope.
    com_addop_varname(struct compiling *, int, char *)
        Emits opcodes for LOAD_DEREF and STORE_DEREF.
    get_ref_type(struct compiling *, char *name)
        Return NAME_CLOSURE if ref type is FREE or CELL
    symtable_load_symbols(struct compiling *)
        Decides what variables are cell or free based on def-use info.
        Can now raise SyntaxError if nested scopes are mixed with
        exec or from blah import *.
    make_scope_info(PyObject *, PyObject *, int, int)
        Helper functions for symtable scope stack.
    symtable_update_free_vars(struct symtable *)
        After a code block has been analyzed, it must check each of
        its children for free variables that are not defined in the
        block.  If a variable is free in a child and not defined in
        the parent, then it is defined by block the enclosing the
        current one or it is a global.  This does the right logic.
    symtable_add_use() is now a macro for symtable_add_def()
    symtable_assign(struct symtable *, node *)
        Use goto instead of for (;;)

    Fixed bug in symtable where name of keyword argument in function
    call was treated as assignment in the scope of the call site. Ex:
        def f():
            g(a=2) # a was considered a local of f

ceval.c
    eval_code2() now take one more argument, a closure.
    Implement LOAD_CLOSURE, LOAD_DEREF, STORE_DEREF, MAKE_CLOSURE>

    Also: When name error occurs for global variable, report that the
    name was global in the error mesage.

Objects/frameobject.c
    Initialize f_closure to be a tuple containing space for cellvars
    and freevars.  f_closure is NULL if neither are present.
Objects/funcobject.c
    Add support for func_closure.
Python/import.c
    Change the magic number.
Python/marshal.c
    Track changes to code objects.

Objects/funcobject.c

@@ -20,6 +20,7 @@ PyFunction_New(PyObject *code, PyObject *globals)
 		op->func_name = ((PyCodeObject *)code)->co_name;
 		Py_INCREF(op->func_name);
 		op->func_defaults = NULL; /* No default arguments */
+		op->func_closure = NULL;
 		consts = ((PyCodeObject *)code)->co_consts;
 		if (PyTuple_Size(consts) >= 1) {
 			doc = PyTuple_GetItem(consts, 0);
@@ -89,6 +90,37 @@ PyFunction_SetDefaults(PyObject *op, PyObject *defaults)
 	return 0;
 }
 
+PyObject *
+PyFunction_GetClosure(PyObject *op)
+{
+	if (!PyFunction_Check(op)) {
+		PyErr_BadInternalCall();
+		return NULL;
+	}
+	return ((PyFunctionObject *) op) -> func_closure;
+}
+
+int
+PyFunction_SetClosure(PyObject *op, PyObject *closure)
+{
+	if (!PyFunction_Check(op)) {
+		PyErr_BadInternalCall();
+		return -1;
+	}
+	if (closure == Py_None)
+		closure = NULL;
+	else if (PyTuple_Check(closure)) {
+		Py_XINCREF(closure);
+	}
+	else {
+		PyErr_SetString(PyExc_SystemError, "non-tuple closure");
+		return -1;
+	}
+	Py_XDECREF(((PyFunctionObject *) op) -> func_closure);
+	((PyFunctionObject *) op) -> func_closure = closure;
+	return 0;
+}
+
 /* Methods */
 
 #define OFF(x) offsetof(PyFunctionObject, x)
@@ -98,6 +130,7 @@ static struct memberlist func_memberlist[] = {
         {"func_globals",  T_OBJECT,     OFF(func_globals),      READONLY},
         {"func_name",     T_OBJECT,     OFF(func_name),         READONLY},
         {"__name__",      T_OBJECT,     OFF(func_name),         READONLY},
+        {"func_closure",  T_OBJECT,     OFF(func_closure)},
         {"func_defaults", T_OBJECT,     OFF(func_defaults)},
         {"func_doc",      T_OBJECT,     OFF(func_doc)},
         {"__doc__",       T_OBJECT,     OFF(func_doc)},