findbar: Hide when pressing Escape

Connect a handler for the GTK stop-search signal, and hide the FindBar
when it is received.

Although there exists code in FileDiff.on_key_event to handle Escape
key presses, Escape key press events are not propagated when the
GtkSearchEntry has focus.

Author: CyberShadow

data/ui/findbar.ui

@@ -137,6 +137,7 @@
             <property name="secondary_icon_activatable">False</property>
             <signal name="changed" handler="on_find_entry_changed" swapped="no"/>
             <signal name="activate" handler="on_find_next_button_clicked" swapped="no"/>
+            <signal name="stop-search" handler="on_stop_search" swapped="no"/>
           </object>
           <packing>
             <property name="left_attach">1</property>

meld/ui/findbar.py

@@ -48,6 +48,9 @@ def hide(self):
         self.wrap_box.set_visible(False)
         self.widget.hide()
 
+    def on_stop_search(self, search_entry):
+        self.hide()
+
     def set_text_view(self, textview):
         self.textview = textview
         if textview is not None: