Add a separate keybinding signal for activating links

Keeping the keybinding signal and the regular signal separate is
cleaner and allows us to pass the uri as a parameter to the
activate-link signal.

docs/reference/gtk/migrating-GtkLabel-links.sgml

@@ -18,9 +18,7 @@
   <para>
     One difference between the two APIs is that the ::url-activated signal
     from SexyUrlLabel has been replaced by the #GtkLabel::activate-link
-    signal. The activated URI is no longer passed as an argument to the
-    signal handler. Instead, call gtk_label_get_current_uri() to obtain it.
-    However, the need for connecting to this signal is greatly reduced,
+    signal. The need for connecting to this signal is greatly reduced,
     since GtkLabel has a default handler that calls gtk_show_uri().
   </para>
 </chapter>

docs/reference/gtk/tmpl/gtklabel.sgml

@@ -174,8 +174,8 @@ attribute is displayed as a tooltip on the link. An example looks like this:
 <informalexample><programlisting>
 gtk_label_set_markup (label, "Go to the &lt;a href=\"http://www.gtk.org\" title=\"&amp;lt;i&amp;gt;Our&amp;/i&amp;gt; website\"&gt;GTK+ website</a> for more...");
 </programlisting></informalexample>
-It is possible to implement custom handling for links with the
-#GtkLabel::activate-link signal and the gtk_label_get_current_uri() function.
+It is possible to implement custom handling for links and their tooltips with
+the #GtkLabel::activate-link signal and the gtk_label_get_current_uri() function.
 </para>
 
 </refsect2>