Use gtk_init_check instead of gtk_init so that we can racefully exit

Use gtk_init_check instead of gtk_init so that we can racefully exit
(i.e. raise an exception in wxPython) instead of just terminating the
app.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@27375 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775