Add some support for numpad shortcuts (#175)

Author: kaiw

data/ui/filediff.ui

@@ -132,6 +132,7 @@
         <signal name="activate" handler="delete_change" swapped="no"/>
       </object>
       <accelerator key="Delete" modifiers="GDK_MOD1_MASK"/>
+      <accelerator key="KP_Delete" modifiers="GDK_MOD1_MASK"/>
     </child>
     <child>
       <object class="GtkAction" id="MergeFromLeft">

meld/meldwindow.py

@@ -189,6 +189,10 @@ def app_action(*args):
         accels.connect(keyval, mask, 0, self.on_menu_edit_down_activate)
         (keyval, mask) = Gtk.accelerator_parse("<Primary>E")
         accels.connect(keyval, mask, 0, self.on_menu_edit_up_activate)
+        (keyval, mask) = Gtk.accelerator_parse("<Alt>KP_Down")
+        accels.connect(keyval, mask, 0, self.on_menu_edit_down_activate)
+        (keyval, mask) = Gtk.accelerator_parse("<Alt>KP_Up")
+        accels.connect(keyval, mask, 0, self.on_menu_edit_up_activate)
         (keyval, mask) = Gtk.accelerator_parse("F5")
         accels.connect(keyval, mask, 0, self.on_menu_refresh_activate)