Small updates to various docs.

Small updates to various docs.

Original commit message from CVS:
* docs/manual/basics-pads.xml:
* docs/plugins/Makefile.am:
* docs/plugins/gstreamer-plugins-docs.sgml:
* docs/plugins/gstreamer-plugins-sections.txt:
* docs/pwg/advanced-clock.xml:
* docs/pwg/advanced-scheduling.xml:
* docs/pwg/advanced-types.xml:
* plugins/elements/gstfdsink.c:
* plugins/elements/gstfdsrc.c:
* plugins/elements/gstfdsrc.h:
* plugins/elements/gstidentity.c: (gst_identity_class_init):
* plugins/elements/gstidentity.h:
* plugins/elements/gstqueue.h:
* plugins/elements/gsttee.c:
* plugins/elements/gsttee.h:
* plugins/elements/gsttypefindelement.c:
(gst_type_find_element_class_init):
* plugins/elements/gsttypefindelement.h:
Small updates to various docs.
Added core plugins to docs.