cell renderer text: Allow entries to shrink

Set a small max-width on entries used for editing cells, so they
adapt to small columns and don't overlap the next column.

https://bugzilla.gnome.org/show_bug.cgi?id=770374

gtk/gtkcellrenderertext.c

@@ -2024,6 +2024,7 @@ gtk_cell_renderer_text_start_editing (GtkCellRenderer      *cell,
 
   gtk_entry_set_has_frame (GTK_ENTRY (priv->entry), FALSE);
   gtk_entry_set_alignment (GTK_ENTRY (priv->entry), xalign);
+  gtk_entry_set_width_chars (GTK_ENTRY (priv->entry), 5);
 
   if (priv->text)
     gtk_entry_set_text (GTK_ENTRY (priv->entry), priv->text);