huge modifications, hope i didn't break something:

huge modifications, hope i didn't break something:

Original commit message from CVS:
huge modifications, hope i didn't break something:
- added functions for setting/getting locked state of elements. gst_element_lock_state syncs the pads state with the state of its parent.
- made all gst_element_link_* functions call gst_element_link_pads_filtered
- gst_element_link_pads_filtered now accepts NULL as a pad name.
- make sure the link functions are only called when the elements are paused
That's it.