guarding scripts with __main__ and doc changes

tox-flakes environment tries to import the modules for
checking, and that may fail because of its dependencies

--HG--
branch : cx_freeze-support

doc/en/example/simple.txt

@@ -703,7 +703,8 @@ must declare them explicitly by using ``pytest.cx_freeze_support.includes()``::
     import pytest
 
     setup(
-        name="runtests",
+        name="app_main",
+        executables=[Executable("app_main.py")],
         options={"build_exe":
             {
             'includes': pytest.cx_freeze_support.includes()}

testing/cx_freeze/runtests_setup.py

@@ -1,6 +1,7 @@
 """
 Sample setup.py script that generates an executable with pytest runner embedded.
 """
+if __name__ == '__main__':
     from cx_Freeze import setup, Executable
     import pytest
 

testing/cx_freeze/tox_run.py

@@ -5,6 +5,7 @@ directory.
 .. note:: somehow calling "build/runtests_script" directly from tox doesn't
           seem to work (at least on Windows).
 """
+if __name__ == '__main__':
     import os
     import sys