Allow "bin/mail send-test" to accept raw email addresses via "--to"

Summary: Ref T12372. This supports testing the wordwrap() patch discussed in that task.

Test Plan:

• Ran bin/mail send-test --to email@domain.com
• Ran bin/mail send-test --to username

Reviewers: chad, lvital

Reviewed By: lvital

Maniphest Tasks: T12372

Differential Revision: https://secure.phabricator.com/D17489