Fixed type conversion from VALUE to GType

  * bug fix for the following errors
    * clutter/lib/clutter.rb:123:in `register_boxed_class_converter': integer 140532096032688 too big to convert to `unsigned int' (RangeError)
    * gobject-introspection/lib/gobject-introspection/loader.rb:177:in `get_field_value': integer 140479269924112 too big to convert to `unsigned int'
Merge pull request #186 from tanahiro/master

Fixed type conversion from VALUE to GType

Patch by Hiroyuki Tanaka. Thanks!!!
Merge pull request #187 from cosmo0920/drop-gtk2.4.0-macro-gtk-part

drop GTK_CHECK_VERSION(2,4,0) macro in gtk2/rbgtk*.c

Patch by cosmo. Thanks!!!
gtk2 rbgtkmenu.c: drop GTK_CHECK_VERSION(2,6,0)
gtk2 rbgtkcellrendererprogress.c: drop GTK_CHECK_VERSION(2,6,0)
gtk2 rbgtkdrag.c: drop GTK_CHECK_VERSION(2,6,0)
gtk2 rbgtkstock.c: drop GTK_CHECK_VERSION(2,6,0)
gtk2 rbgtkfilechooserbutton.c: drop GTK_CHECK_VERSION(2,6,0)
gtk2 rbgtkicontheme.c: drop GTK_CHECK_VERSION(2,6,0)
gtk2 rbgtkselectiondata.c: drop GTK_CHECK_VERSION(2,6,0)
gtk2 rbgtkliststore.c: drop GTK_CHECK_VERSION(2,6,0)
gtk2 rbgdkdragcontext.c: drop GTK_CHECK_VERSION(2,6,0)
gtk2 rbgtktreeview.c: drop GTK_CHECK_VERSION(2,6,0)
gtk2 rbgtkcellrenderercombo.c: drop GTK_CHECK_VERSION(2,6,0)
gtk2 rbgtkentrycompletion.c: drop GTK_CHECK_VERSION(2,6,0)
gtk2 rbgtkdialog.c: drop GTK_CHECK_VERSION(2,6,0)
gtk2 rbgtkcombobox.c: drop GTK_CHECK_VERSION(2,6,0)
gtk2 rbgtktextbuffer.c: drop GTK_CHECK_VERSION(2,6,0)
gtk2 rbgdkwindow.c: drop GTK_CHECK_VERSION(2,6,0)
gtk2 rbgtktextview.c: drop GTK_CHECK_VERSION(2,6,0)