imap-send: display the destination mailbox when sending a message

imap-send: display the destination mailbox when sending a message

Whenever we sent a message using the `imap-send` command, it would
display a log showing the number of messages which are to be sent.
For example:

    sending 1 message
     100% (1/1) done

This had been made more informative by adding the name of the destination
folder as well:

    Sending 1 message to Drafts folder...
     100% (1/1) done

Signed-off-by: Aditya Garg <gargaditya08@live.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>