Allow referencing all PyConstNodes in nogil expressions, e.g. in 'is' tests (because, why not?).

Cython/Compiler/ExprNodes.py

@@ -1167,6 +1167,7 @@ class PyConstNode(AtomicExprNode):
 
     is_literal = 1
     type = py_object_type
+    nogil_check = None
 
     def is_simple(self):
         return 1
@@ -1192,8 +1193,6 @@ class NoneNode(PyConstNode):
 
     constant_result = None
 
-    nogil_check = None
-
     def compile_time_value(self, denv):
         return None
 

tests/errors/nogil.pyx

@@ -105,14 +105,10 @@ _ERRORS = u"""
 31:16: Constructing complex number not allowed without gil
 33:8: Assignment of Python object not allowed without gil
 33:14: Backquote expression not allowed without gil
-33:15: Operation not allowed without gil
 34:15: Assignment of Python object not allowed without gil
-34:15: Operation not allowed without gil
 34:15: Python import not allowed without gil
-35:8: Operation not allowed without gil
 35:13: Python import not allowed without gil
 35:25: Constructing Python list not allowed without gil
-35:25: Operation not allowed without gil
 36:17: Iterating over Python object not allowed without gil
 38:11: Discarding owned Python object not allowed without gil
 38:11: Indexing Python object not allowed without gil