Fix icon position saving on resolution change (Bug 10813)

This patch does the following:
 1) Alter the SAVE_DELAY factor from 7 seconds to 1 second, so that when you
    change/move some icon on the desktop, you don't have to wait 7 seconds
    before xfdesktop saves the icons and you can safely logout.
 2) When you change your screen resolution with one never used so far,
    now xfdesktop will save your icon positions even if you don't change
    the icons positions.

Signed-off-by: Eric Koegel <eric.koegel@gmail.com>
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