gst/: Simplify pad activation.

gst/: Simplify pad activation.

Original commit message from CVS:
* gst/base/Makefile.am:
* gst/base/README:
* gst/base/gstbasesink.c: (gst_basesink_get_type),
(gst_basesink_base_init), (gst_basesink_class_init),
(gst_basesink_pad_getcaps), (gst_basesink_init),
(gst_basesink_activate), (gst_basesink_change_state):
* gst/base/gstbasesink.h:
* gst/base/gstbasetransform.c: (gst_base_transform_get_type),
(gst_base_transform_base_init), (gst_base_transform_finalize),
(gst_base_transform_class_init), (gst_base_transform_init),
(gst_base_transform_proxy_getcaps), (gst_base_transform_setcaps),
(gst_base_transform_event), (gst_base_transform_getrange),
(gst_base_transform_chain), (gst_base_transform_handle_buffer),
(gst_base_transform_set_property),
(gst_base_transform_get_property),
(gst_base_transform_sink_activate),
(gst_base_transform_src_activate),
(gst_base_transform_change_state):
* gst/base/gstbasetransform.h:
* gst/elements/gstidentity.c: (gst_identity_finalize),
(gst_identity_class_init), (gst_identity_init),
(gst_identity_event), (gst_identity_check_perfect),
(gst_identity_transform), (gst_identity_set_property),
(gst_identity_get_property), (gst_identity_change_state):
* gst/elements/gstidentity.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_check_pull_range), (gst_pad_pull_range):
* gst/gstpad.h:
Simplify pad activation.
Added function to check if pull_range can be performed.
Error out when pulling inactive or flushing pads.
Removed const from refcounted types as it does not make sense.
Simplify pad templates in basesink
Added base class for simple 1-to-1 transforms.
Make identity subclass the base transform.