Current stgit asks SMTP password for every patch

Hello, Alex!

I was unpleasantly surprised when the current STGit started asking me
for the SMTP password for every patch in the series:

$ stg mail --to minicom ncurses-const..clobber
Checking the validity of the patches ... done
Sending patch "ncurses-const" ... Please enter SMTP password: 
done
Sending patch "precision-int" ... Please enter SMTP password: 
done
Sending patch "aliasing" ... Please enter SMTP password: 
done
Sending patch "clobber" ... Please enter SMTP password: 
done

The code in __send_message_smtp() lacks any caching for the smtppassword
variable.  The code comes from your commit
89d7ec43e0b25cc6cbc9feb044d7ce7048f224eb
stg mail: Refactor __send_message and friends

Ideally, asking for the password (as well as other verification of the
e-mail credentials) should be done before "Sending patch" is shown, and
before the cover letter if any.  That is, it should be in func() in
stgit/commands/mail.py.

But I'll also be fine with a simple-minded password caching in
__send_message_smtp().

-- 
Regards,
Pavel Roskin