Please describe the problem:
If you select a folder in Evolution and change the value of
/apps/evolution/mail/display/show_preview through gconf-editor, the evolution
does nothing to reflect the change.

Steps to reproduce:
1. Open evolution and select a folder, such as Inbox.
2. Open gconf-editor and select /apps/evolution/mail/display/show_preview.
3. If the folder already has a preview pane, set show_preview to False.
Otherwise, set True.


Actual results:
The folder doesn't show/hide the preview pane even if you have set show_preview
to True/False.

Expected results:
The folder should show/hide its preview pane when setting show_previw to True/False.

Does this happen every time?
Yes

Other information:
It helps central management if Evolution respect to show_previw's change in gconf.