Fix logic a bit - avoid dereferencing NULL pointer

Closes https://github.com/mate-desktop/mate-panel/pull/257
clock: Use lists instead of arrays

Closes https://github.com/mate-desktop/mate-panel/pull/258
Sync translations with transifex
Bump version to 1.9.3
na: Fix handling of SYSTEM_TRAY_CANCEL_MESSAGE

We were not looking at the right field for the message ID: the ID is in
the 4th field for BEGIN_MESSAGE, but 2nd field for CANCEL_MESSAGE.

Taken from gnome-panel commit: 8ff843458425d525b10fc5d9b7bb357248c637c8
From: Vincent Untz <vuntz@gnome.org>
gdk_x11_window_lookup_for_display was added in Gtk+2.24

So cut down on the ifdef hell a bit.
panel-menu-botton: small white-space fix
button-widget: small white-space cleanup
panel-addto: Remove the vbox as it is redundant.

And cut down on some ifdef hell in the process.
Gtk3: Replaced gdk_cursor_unref() by g_object_unref()

gdk_cursor_unref () is deprecated in Gtk+3
Gtk3: Fix use of deprecated gdk_display_get_pointer()

Replaced gdk_display_get_pointer() by gdk_device_get_position()

Taken from gnome-panel commit: c5111b57d5241f8e4e9f420df1a904f66fa2e89d
From: Germán Póo-Caamaño <gpoo@gnome.org>
Small white-space fix
Gtk3: Fix use of deprecated gdk_pointer_grab()/_ungrab()

Replaced gdk_pointer_grab() and gdk_pointer_ungrab()
by gdk_device_grab() and gdk_device_ungrab(), respectively.

Taken from gnome-panel commit: 98da5c1953ab90cc5581c1858d7a9c3d3cf796eb
From: Germán Póo-Caamaño <gpoo@gnome.org>
Gtk3: Fix use of pending deprecated gdk_pointer_grab()/_ungrab()

eplaced gdk_pointer_grab() and gdk_pointer_ungrab()
by gdk_device_grab() and gdk_device_ungrab(), respectively.

Based on gnome-panel commit: eff5d569c162d508f996678f0d1ea8647c1b810d
From: Germán Póo-Caamaño <gpoo@gnome.org>
Fix implicit declaration of function of gdk_x11_set_sm_client_id

We now use it for both Gtk+2 and Gtk+3
Add a gtkimage with the current pixbuf to button-widget

We need to add a child to the button to get the right allocation of the
pixbuf. When the button is created without a pixbuf,
get_preferred_width/height are called the first time when the widget is
allocated and 0x0 size is cached by gtksizerequest. Since the widget
doesn't change its size when a pixbuf is set, gtk_widget_queue_resize()
always uses the cached values instead of calling
get_preferred_width_height() again. So the actual size, based on pixbuf
size, is never used. We are overriding the draw() method, so having a
child doesn't affect the widget rendering anyway.

Taken from gnome-panel commit: 0b8ace11087855d741cdeed97dc839db50319ae8
from: Carlos Garcia Campos <carlosgc@gnome.org>
Gtk3: Remove border of panel menu bar

Taken from gnome-panel commit: d47c8957a1b7079891dee37b361694fce17b6b53
From: Carlos Garcia Campos <carlosgc@gnome.org>
Gtk3: window-list Don't use deprecated size-allocate signal

Take an additional change from gnome-panel that was not in MATE
commit: 77a45f0abf8d0db41bb4b99e08dfbdd968cb6be8
From: Carlos Garcia Campos <carlosgc@gnome.org>
Gtk3: Remove frame of window-menu applet

Based on gnome-panel commit: 1f086d72760569bc466de082e99a55a82ac06014
From: Carlos Garcia Campos <carlosgc@gnome.org>
Gtk3: button-widget: Port to GtkStyleContext

Based on gnome-panel commit: ee0fcd193030b433b5aa1785a864f89e25345f01
From: Carlos Garcia Campos <carlosgc@gnome.org>

In the process make button_widget_{draw,expose} a little more readable.