Add --inspect-emails option

Suggested-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>
Only undo to staging if there was a cover letter

If this is a patch without a cover letter, don't create a staging tag.
The staging tag would cause an unwanted cover letter to be created when
the user retries.

Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>