- Regenerate IN module for most recent maintenance tree of FreeBSD 6 and 7.

2. Refactor to use more descriptive names.
3. Enhance tests in main().

now idempotent.

See issue 1324.

in response that keeped having a non-ascii character.

Neal: please backport!

When "MAIL" is received without args, an exception happens instead of
sending a 501 syntax error response.

while another thread uses it.