bug#21969: VC opens new window to display minimal messages

[David Reitter]

At some point on the way to Emacs 25, VC has begun creating new windows to 
display messages that would more appropriately fit into the echo area.

For example, you do C-x =, it’ll display a “no revisions between working 
revision and work file” message.  But that is shown in the echo area AND a 
newly created window.

The consequence is that the user has to get rid of the superfluous mini window. 
 Also, mistakes happen - i.e., opening a new file, the new buffer will display 
in a window that is only one line high, so one’s got to deal with that.

Bottomline, this shouldn’t happen.  Use the echo area appropriately unless 
there’s really something to display.