gtk2 rbgdkcursor.c: drop GTK_CHECK_VERSION(2,4,0)
gtk2 rbgdkwindow.c: drop GTK_CHECK_VERSION(2,4,0)
gtk2 rbgdkdraw.c: drop GTK_CHECK_VERSION(2,4,0)
gtk2 rbgdkscreen.c: drop GTK_CHECK_VERSION(2,4,0)
gtk2 rbgdkdisplay.c: drop GTK_CHECK_VERSION(2,4,0)
Merge pull request #185 from cosmo0920/drop-gtk2.4.0-macro-gdk-part

drop GTK_CHECK_VERSION(2,4,0) macro in gtk2/rbgdk*.c

Patch by cosmo. Thanks!!!