emerge -av --oneshot --tree =gnome-base/gnome-settings-daemon-2.22.2.1 =mail-client/evolution-2.22.3.1 =gnome-base/gnome-control-center-2.22.2.1

These are the packages that would be merged, in reverse order:

Calculating dependencies... done!
[ebuild   R   ] gnome-base/gnome-control-center-2.22.2.1  USE="hal -debug -eds -esd" 0 kB
[ebuild   R   ] mail-client/evolution-2.22.3.1  USE="crypt dbus* hal* ipv6 kerberos spell ssl -debug -krb4 -ldap -mono -networkmanager -nntp -pda -profile" 0 kB
[ebuild   R   ] gnome-base/gnome-settings-daemon-2.22.2.1  USE="alsa -debug -esd -gstreamer" 0 kB

Total: 3 packages (3 reinstalls), Size of downloads: 0 kB

Would you like to merge these packages? [Yes/No] No