R1:80b23b21f396

Work around mailparse bug (?) with messages that have no terminal newline

Summary: Under some unusual circumstances, mailparse appears to incorrectly discard the last line of some mail messages.

Test Plan:
- Constructed a raw mail with no terminal newline.
- Piped it into `mail_receiver.php`.
- Saw the last line vanish into the aether.
- Applied patch; repeated; last line survived.

Reviewers: btrahan, chad

Reviewed By: chad

Subscribers: chad, epriestley

Differential Revision: https://secure.