gst/gstbin.*: 'private' is a c++ keyword, let's not use that in header files, otherwise c++ compilers will throw a ta...

Original commit message from CVS:
* gst/gstbin.c: (gst_bin_init), (gst_bin_dispose),
(gst_bin_set_property), (gst_bin_get_property),
(gst_bin_remove_func), (gst_bin_handle_message_func):
* gst/gstbin.h:
'private' is a c++ keyword, let's not use that in header files,
otherwise c++ compilers will throw a tantrum.