Part way to allowing "from __future__ import generators" to communicate
that info to code dynamically compiled *by* code compiled with generators
enabled.  Doesn't yet work because there's still no way to tell the parser
that "yield" is OK (unlike nested_scopes, the parser has its fingers in
this too).
Replaced PyEval_GetNestedScopes by a more-general
PyEval_MergeCompilerFlags.  Perhaps I should not have?  I doubted it was
*intended* to be part of the public API, so just did.
diff --git a/Include/Python.h b/Include/Python.h
index 5d91125..24d33b2 100644
--- a/Include/Python.h
+++ b/Include/Python.h
@@ -96,8 +96,8 @@
 #include "pystate.h"
 
 #include "modsupport.h"
-#include "ceval.h"
 #include "pythonrun.h"
+#include "ceval.h"
 #include "sysmodule.h"
 #include "intrcheck.h"
 #include "import.h"