Useful future statement support for the interactive interpreter

(Also remove warning about module-level global decl, because we can't
distinguish from code passed to exec.)

Define PyCompilerFlags type contains a single element,
cf_nested_scopes, that is true if a nested scopes future statement has
been entered at the interactive prompt.

New API functions:
    PyNode_CompileFlags()
    PyRun_InteractiveOneFlags()
    -- same as their non Flags counterparts except that the take an
       optional PyCompilerFlags pointer

compile.c: In jcompile() use PyCompilerFlags argument.  If
    cf_nested_scopes is true, compile code with nested scopes.  If it
    is false, but the code has a valid future nested scopes statement,
    set it to true.

pythonrun.c: Create a new PyCompilerFlags object in
    PyRun_InteractiveLoop() and thread it through to
    PyRun_InteractiveOneFlags().
diff --git a/Include/pythonrun.h b/Include/pythonrun.h
index 13ed471..3f9f70b 100644
--- a/Include/pythonrun.h
+++ b/Include/pythonrun.h
@@ -7,6 +7,10 @@
 extern "C" {
 #endif
 
+typedef struct {
+	int cf_nested_scopes;
+} PyCompilerFlags;
+
 DL_IMPORT(void) Py_SetProgramName(char *);
 DL_IMPORT(char *) Py_GetProgramName(void);
 
@@ -26,6 +30,7 @@
 DL_IMPORT(int) PyRun_SimpleFile(FILE *, char *);
 DL_IMPORT(int) PyRun_SimpleFileEx(FILE *, char *, int);
 DL_IMPORT(int) PyRun_InteractiveOne(FILE *, char *);
+DL_IMPORT(int) PyRun_InteractiveOneFlags(FILE *, char *, PyCompilerFlags *);
 DL_IMPORT(int) PyRun_InteractiveLoop(FILE *, char *);
 
 DL_IMPORT(struct _node *) PyParser_SimpleParseString(char *, int);