bpo-38914 Do not require email field in setup.py. (GH-17388)



When checking `setup.py` and when the `author` field was provided, but
the `author_email` field was missing, erroneously a warning message was
displayed that the `author_email` field is required.

The specs do not require the `author_email`field:
https://packaging.python.org/specifications/core-metadata/#author

The same is valid for `maintainer` and `maintainer_email`.

The warning message has been adjusted.

modified:   Doc/distutils/examples.rst
modified:   Lib/distutils/command/check.py


https://bugs.python.org/issue38914
diff --git a/Doc/distutils/examples.rst b/Doc/distutils/examples.rst
index 44f7083..e492b7f 100644
--- a/Doc/distutils/examples.rst
+++ b/Doc/distutils/examples.rst
@@ -255,7 +255,7 @@
     running check
     warning: check: missing required meta-data: version, url
     warning: check: missing meta-data: either (author and author_email) or
-             (maintainer and maintainer_email) must be supplied
+             (maintainer and maintainer_email) should be supplied
 
 
 If you use the reStructuredText syntax in the ``long_description`` field and