** READ BEFORE APPLYING **

This patch changes the behaviour of the folder-browser a little bit:

a) It adds support for browsing the list up and down by using the K and J keys.

b) The default is to load and display a message as soon as it's entry in the
list has been selected. This is annoying when browsing using the keyboard and
pressing down CTRL when navigating isn't too handy either. This patch makes
evolution only load and display a message after Return or KP_Enter has been
pressed on the message list.
This quickhack has a 'sideeffect' too: it's not possible to read a message
using a mouse click other than the default double_click behaviour which opens a
new window for the message's body.