[gtkmm] Gtk::TreeIter<>: Fix operator==() and operator!=()

[Murray Cumming <murrayc src gnome org>]

commit f1b0ec4da726c7ee8042349795d7b374add33a2f
Author: Kjell Ahlstedt <kjell ahlstedt bredband net>
Date:   Tue Mar 14 16:45:15 2017 +0100

    Gtk::TreeIter<>: Fix operator==() and operator!=()
    
    It shall be possible to compare a TreeModel::iterator with a TreeModel::
    const_iterator, i.e. a TreeIter<TreeRow> with a TreeIter<TreeConstRow>.
    Let the comparison operators take const TreeIterBase3&.
    TreeIterBase3 is a base class of TreeIter<>. Bug 134520

 gtk/src/treeiter.hg |    6 ++----
 1 files changed, 2 insertions(+), 4 deletions(-)
---
diff --git a/gtk/src/treeiter.hg b/gtk/src/treeiter.hg
index bd38b79..23e385e 100644
--- a/gtk/src/treeiter.hg
+++ b/gtk/src/treeiter.hg
@@ -254,13 +254,11 @@ public:
 }; // class TreeIter<>
 
 /** @relates Gtk::TreeIter */
-template <typename T>
-inline bool operator==(const TreeIter<T>& lhs, const TreeIter<T>& rhs)
+inline bool operator==(const TreeIterBase3& lhs, const TreeIterBase3& rhs)
 { return lhs.equal(rhs); }
 
 /** @relates Gtk::TreeIter */
-template <typename T>
-inline bool operator!=(const TreeIter<T>& lhs, const TreeIter<T>& rhs)
+inline bool operator!=(const TreeIterBase3& lhs, const TreeIterBase3& rhs)
 { return !lhs.equal(rhs); }
 
 template <typename RowType, typename ColumnType>