- change references from configure.in to configure.ac

This also affected smtplib.SMTP.send_message, which calls BytesParser.

In Python2, if a unicode string was assigned as the value of a header,
email would automatically CTE encode it using the UTF8 charset.
This capability was lost in the Python3 translation, and this patch
restores it.

Patch by Ali Ikinci, assisted by R. David Murray.

I also added a fix for the mailbox test that was depending (with a comment
that it was a bad idea to so depend) on non-ASCII causing message_from_string
to raise an error.  It now uses support.patch to induce an error during
message serialization.

Patch by Roger Serwy.

Mac OS X to prevent interpreter crashes when compiled on 10.7.

str.format_map tests don't do what they say: fix to actually implement the intent of the test. Closes #13450.

Issue #14252: Fix subprocess.Popen.terminate() to not raise an error under Windows when the child process has already exited.

Patch from Armin, test from me.