gst/: More work on the generic source base class, implement seeking, query.

gst/: More work on the generic source base class, implement seeking, query.

Original commit message from CVS:
* gst/base/README:
* gst/base/gstbasesrc.c: (gst_basesrc_get_type),
(gst_basesrc_init), (gst_basesrc_get_formats), (gst_basesrc_query),
(gst_basesrc_get_event_mask), (gst_basesrc_do_seek),
(gst_basesrc_event_handler), (gst_basesrc_get_range_unlocked),
(gst_basesrc_check_get_range), (gst_basesrc_loop),
(gst_basesrc_unlock), (gst_basesrc_get_size), (gst_basesrc_start),
(gst_basesrc_stop), (gst_basesrc_activate),
(gst_basesrc_change_state), (basesrc_find_peek),
(basesrc_find_suggest), (gst_basesrc_type_find):
* gst/base/gstbasesrc.h:
* gst/elements/gstfilesrc.c: (gst_filesrc_base_init),
(gst_filesrc_class_init), (gst_filesrc_init),
(gst_filesrc_finalize), (gst_filesrc_set_location),
(gst_filesrc_set_property), (gst_filesrc_get_property),
(gst_filesrc_free_parent_mmap), (gst_filesrc_map_region),
(gst_filesrc_map_small_region), (gst_filesrc_create_mmap),
(gst_filesrc_create_read), (gst_filesrc_create),
(gst_filesrc_get_size), (gst_filesrc_start), (gst_filesrc_stop):
* gst/elements/gstfilesrc.h:
* gst/gstelement.c: (gst_element_get_state_func),
(gst_element_lost_state), (gst_element_pads_activate):
* gst/gstpad.c: (gst_pad_set_active), (gst_pad_peer_set_active),
(gst_pad_set_checkgetrange_function), (gst_pad_check_pull_range),
(gst_pad_pull_range):
* gst/gstpad.h:
More work on the generic source base class, implement seeking,
query.
Make filesrc extend the base source class.
Added gst_pad_set_checkgetrange_function to GstPad.