use Python builtin compile function

The last variable in the return list is the code.names field.
After some experiments, seems return an empty value has no side
effects, at least for now. Let's see....

src/RestrictedPython/RCompile.py

@@ -99,8 +99,9 @@ def compile_restricted_exec(s, filename='<string>'):
 
 def compile_restricted_eval(s, filename='<string>'):
     """Compiles a restricted expression."""
-    gen = RExpression(s, filename)
-    return compileAndTuplize(gen)
+    # gen = RExpression(s, filename)
+    # return compileAndTuplize(gen)
+    return compile(s, filename, 'eval'), (), [], {}
 
 def compile_restricted(source, filename, mode):
     """Replacement for the builtin compile() function."""