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

Calculating dependencies... done!
[ebuild     U ~] dev-libs/glib-2.36.4-r1:2 [2.32.4-r1:2] USE="-debug (-fam) (-selinux) -static-libs -systemtap {-test} -utils -xattr" ABI_X86="(64%*) -32% (-x32)" PYTHON_TARGETS="python2_7%* -python2_6%" 8,303 kB
[ebuild  N     ] gnome-base/gvfs-1.12.3-r1  USE="udev -afp -archive -avahi -bluetooth -bluray -cdda -doc -fuse -gdu -gnome-keyring -gphoto2 -http -ios -samba (-udisks)" 0 kB
[ebuild  N    ~] gnome-base/gvfs-1.16.3-r1  USE="gtk udev udisks -afp -archive -avahi -bluetooth -bluray -cdda -fuse -gdu -gnome-keyring -gnome-online-accounts -gphoto2 -http -ios -mtp -samba -systemd {-test}" 1,459 kB
[ebuild  N     ] xfce-base/thunar-1.6.2  USE="dbus libnotify pcre udev -debug -exif -startup-notification {-test}" XFCE_PLUGINS="trash" 1,908 kB

Total: 4 packages (1 upgrade, 3 new), Size of downloads: 11,668 kB

!!! Multiple package instances within a single package slot have been pulled
!!! into the dependency graph, resulting in a slot conflict:

gnome-base/gvfs:0

  (gnome-base/gvfs-1.12.3-r1::gentoo, ebuild scheduled for merge) pulled in by
    (no parents that aren't satisfied by other packages in this slot)

  (gnome-base/gvfs-1.16.3-r1::gentoo, ebuild scheduled for merge) pulled in by
    >=gnome-base/gvfs-1.10.1[udisks,udev] required by (xfce-base/thunar-1.6.2::gentoo, ebuild scheduled for merge)

dev-libs/glib:2

  (dev-libs/glib-2.32.4-r1::gentoo, installed) pulled in by
    <dev-libs/glib-2.33:2 required by (dev-libs/gobject-introspection-1.32.1::gentoo, installed)

  (dev-libs/glib-2.36.4-r1::gentoo, ebuild scheduled for merge) pulled in by
    >=dev-libs/glib-2.35:2 required by (gnome-base/gvfs-1.16.3-r1::gentoo, ebuild scheduled for merge)


It may be possible to solve this problem by using package.mask to
prevent one of those packages from being selected. However, it is also
possible that conflicting dependencies exist such that they are
impossible to satisfy simultaneously.  If such a conflict exists in
the dependencies of two different packages, then those packages can
not be installed simultaneously. You may want to try a larger value of
the --backtrack option, such as --backtrack=30, in order to see if
that will solve this conflict automatically.

For more information, see MASKED PACKAGES section in the emerge man
page or refer to the Gentoo Handbook.


The following keyword changes are necessary to proceed:
 (see "package.accept_keywords" in the portage(5) man page for more details)
# required by x11-libs/vte-0.28.2-r204
# required by x11-terms/xfce4-terminal-0.4.8
# required by @selected
# required by @world (argument)
=dev-libs/glib-2.36.4-r1 ~amd64
# required by xfce-base/thunar-1.6.2[udev]
# required by thunar (argument)
=gnome-base/gvfs-1.16.3-r1 ~amd64

Use --autounmask-write to write changes to config files (honoring
CONFIG_PROTECT). Carefully examine the list of proposed changes,
paying special attention to mask or keyword changes that may expose
experimental or unstable packages.