Make date/timezone validation in changelog.add more robust. Add test.

Validate user input of dates when adding a changelog entry.

Add doc string for debugrename.

Fortify the recognition of a diff header.

Add -p to incoming and outgoing commands to show patch

Revert changeset 120aa5fc7ced1bf765b4f025f5a3a138cd87f49e. I inadvertantly used "hg import" on a message I saved, expecting it to do the right thing, but instead it made the commit look like I authored it, and filled the description with the email header. Changeset 737f9b90c571b3991f7e35dc846e7ef38a475cfe contains a guard against "hg import" doing this again.