[MERGE] Make mail-to address in ``bzr send`` optional for interactive mail clients

[Aaron Bentley]

Aaron Bentley has voted comment.
Status is now: Waiting
Comment:
I think this is a great improvement-- it's now mostly following the rule 
"Easier to ask forgiveness than permission".  But can't we follow it all 
the way and remove the is_interactive check from cmd_send?  We'd just 
rely on mail_client.compose_merge_request to raise 
NoMailAddressSpecified.  is_interactive could go away, or at least 
become private.

For details, see: 
http://bundlebuggy.aaronbentley.com/request/%3C1196112876.5809.30.camel%40laptop%3E