Make _pyrepl not to use the __main__ module as the namespace

The `__main__` module imported in the `_pyrepl` module points to the `_pyrepl` module itself when the interpreter was launched without `-m` option and didn't execute a module,
while it's an unexpected behavior that `__main__` can be `_pyrepl` and relative imports such as `from . import *` works based on the `_pyrepl` module.

Author: whitphx

Lib/_pyrepl/main.py

@@ -1,6 +1,7 @@
 import errno
 import os
 import sys
+import types
 
 
 CAN_USE_PYREPL: bool
@@ -32,9 +33,8 @@ def interactive_console(mainmodule=None, quiet=False, pythonstartup=False):
     if mainmodule:
         namespace = mainmodule.__dict__
     else:
-        import __main__
+        __main__ = types.ModuleType("__main__")
         namespace = __main__.__dict__
-        namespace.pop("__pyrepl_interactive_console", None)
 
     # sys._baserepl() above does this internally, we do it here
     startup_path = os.getenv("PYTHONSTARTUP")