Patch #2477: Added from __future__ import unicode_literals

The new PyParser_*Ex() functions are based on Neal's suggestion and initial patch. The new __future__ feature makes all '' and r'' unicode strings. b'' and br'' stay (byte) strings.
diff --git a/Include/compile.h b/Include/compile.h
index d703edb..43a470d 100644
--- a/Include/compile.h
+++ b/Include/compile.h
@@ -25,6 +25,7 @@
 #define FUTURE_ABSOLUTE_IMPORT "absolute_import"
 #define FUTURE_WITH_STATEMENT "with_statement"
 #define FUTURE_PRINT_FUNCTION "print_function"
+#define FUTURE_UNICODE_LITERALS "unicode_literals"
 
 
 struct _mod; /* Declare the existence of this type */