gst/gstiterator.h: Add some includes.

gst/gstiterator.h: Add some includes.

Original commit message from CVS:
2005-05-09  Andy Wingo  <wingo@pobox.com>

* gst/gstiterator.h: Add some includes.

* gst/gstqueryutils.h: Include more headers.

* gst/gstpad.h:
* gst/gstpad.c (gst_pad_query_position): New routine, replaces
some uses of gst_pad_query.

* gst/gstqueryutils.c: Build fixes. Make parse functions ignore
NULL out parameters.
(gst_query_new_position): New proc, allocates a new position
query.

* gst/Makefile.am (libgstreamer_@GST_MAJORMINOR@_la_SOURCES): Add
gstqueryutils.c to the build.

* gst/gststructure.c (gst_structure_set_valist): Implement with
the generic G_VALUE_COLLECT.