gdesktopappinfo: Add g_desktop_app_info_launch_uris_as_manager()

A new GDesktopAppInfo specific function which provides more control
over launched processes.  Intended basically only for use in GNOME
Shell, where we want:

*) To directly know the GPid for each launched program, without
   having to listen to a DBus signal emitted in our own process
*) Possibly control over the process environment; for example,
   we may want to call setsid() or redirect file descriptors.

And in the future:
*) To avoid recursively calling ourself via DBus, when a later
   patch causes g_app_info_launch() to indirect via the shell.

https://bugzilla.gnome.org/show_bug.cgi?id=606960

gio/gdesktopappinfo.h

@@ -93,6 +93,30 @@ GType     g_desktop_app_info_lookup_get_type                   (void) G_GNUC_CON
 GAppInfo *g_desktop_app_info_lookup_get_default_for_uri_scheme (GDesktopAppInfoLookup *lookup,
                                                                 const char            *uri_scheme);
 
+/**
+ * GDesktopAppLaunchCallback:
+ * @appinfo: a #GDesktopAppInfo
+ * @pid: Process identifier
+ * @user_data: User data
+ *
+ * During invocation, g_desktop_app_info_launch_uris_as_manager() may
+ * create one or more child processes.  This callback is invoked once
+ * for each, providing the process ID.
+ */
+typedef void (GDesktopAppLaunchCallback) (GDesktopAppInfo  *appinfo,
+					  GPid              pid,
+					  gpointer          user_data);
+
+gboolean    g_desktop_app_info_launch_uris_as_manager (GDesktopAppInfo            *appinfo,
+						       GList                      *uris,
+						       GAppLaunchContext          *launch_context,
+						       GSpawnFlags                 spawn_flags,
+						       GSpawnChildSetupFunc        setup,
+						       gpointer                    user_setup_data,
+						       GDesktopAppLaunchCallback   callback,
+						       gpointer                    pid_callback_data,
+						       GError                    **error);
+
 #endif /* G_DISABLE_DEPRECATED */
 
 G_END_DECLS