check/gst/gstbin.c: Added checks for hierarchy consistency whan adding linked element...

check/gst/gstbin.c: Added checks for hierarchy consistency whan adding linked elements to bins.

Original commit message from CVS:
* check/gst/gstbin.c: (GST_START_TEST), (gst_bin_suite):
Added checks for hierarchy consistency whan adding linked
elements to bins.

* check/gst/gstelement.c: (GST_START_TEST), (gst_element_suite):
Added check to test element scheduling without bin/pipeline.

* check/pipelines/simple_launch_lines.c: (GST_START_TEST):
First add elements to bin, then link.

* gst/gstbin.c: (unlink_pads), (gst_bin_add_func),
(gst_bin_remove_func):
Unlink pads from elements added/removed from bin to maintain
hierarchy consistency.