new editwin had message-sending regression with . followed by only blank lines

[nygren@MIT.EDU]

A common case that seems to happen with editing messages results in some extra spaces or newlines at the end of a message buffer, and with the user cursoring up into the message and then ending with a "." on a line by itself. In this case, there may be lines after the "."-line which contain only whitespace (and are thus content-free and invisible to the user). In the previous version of the editwin, we allowed a "." on a line by itself to terminate-and-send a message if the subsequent lines contained only whitespace.

[nelhage@mit.edu]

Fixed by 4ccd92c0e8e17390ecbe280aa90c70b2bf07afd8