check/gst/gstbin.c: since we don't know when preroll is done, use refcount range...

check/gst/gstbin.c: since we don't know when preroll is done, use refcount range check for the sink

Original commit message from CVS:

* check/gst/gstbin.c: (GST_START_TEST):
since we don't know when preroll is done, use refcount range
check for the sink
* gst/check/gstcheck.h:
add macro for checking refcount range