[gtkmm-documentation] Fix the Popover example with --enable-warnings=fatal

[Kjell Ahlstedt <kjellahl src gnome org>]

commit a3df8d970195bb18723d044e74f5938256f9d85b
Author: Kjell Ahlstedt <kjell ahlstedt bredband net>
Date:   Thu Apr 3 14:38:19 2014 +0200

    Fix the Popover example with --enable-warnings=fatal
    
    * examples/book/popover/examplewindow.cc: Swap entries in the constructor's
    initialization list. The order shall be the same as in the .h file, or else
    'make check' fails when --enable-warnings=fatal.

 examples/book/popover/examplewindow.cc |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/examples/book/popover/examplewindow.cc b/examples/book/popover/examplewindow.cc
index b22eef9..0032561 100644
--- a/examples/book/popover/examplewindow.cc
+++ b/examples/book/popover/examplewindow.cc
@@ -22,8 +22,8 @@ ExampleWindow::ExampleWindow()
    m_toggle_form_popover(m_toggle_button),
    m_toggle_form_label("Non-modal Popover"),
    m_toggle_form_combo_label("Popover position:"),
-   m_calendar_popover_label("Label:"),
-   m_calendar_popover(m_calendar)
+   m_calendar_popover(m_calendar),
+   m_calendar_popover_label("Label:")
 {
   // Window properties
   set_title("Popover Example");