Now LyX closes the current document WA only by default (other WAs remain open).

Now LyX closes the current document WA only by default (other WAs remain open).

If the WA is the last one showing a buffer, then the buffer may either be
closed or kept hidden, or the user is asked. The behaviour is controlled
by a new preference option.
For discussion, see http://comments.gmane.org/gmane.editors.lyx.devel/142638