docs: use docbook markup for xi:include

It turns out that the change in gtk-doc-1.20 which wraps the |[]| content in
CDATA break xi:inlcude examples. As in a whole jhbuild checkout these where
the only 4, we're fixing them instead.

gst/audiofx/audiofirfilter.c

@@ -39,9 +39,9 @@
  *
  * <refsect2>
  * <title>Example application</title>
- * |[
+ * <informalexample><programlisting language="C">
  * <xi:include xmlns:xi="http://www.w3.org/2003/XInclude" parse="text" href="../../../../tests/examples/audiofx/firfilter-example.c" />
- * ]|
+ * </programlisting></informalexample>
  * </refsect2>
  */
 

gst/audiofx/audioiirfilter.c

@@ -35,9 +35,9 @@
  *
  * <refsect2>
  * <title>Example application</title>
- * |[
+ * <informalexample><programlisting language="C">
  * <xi:include xmlns:xi="http://www.w3.org/2003/XInclude" parse="text" href="../../../../tests/examples/audiofx/iirfilter-example.c" />
- * ]|
+ * </programlisting></informalexample>
  * </refsect2>
  */
 

gst/level/gstlevel.c

@@ -93,9 +93,9 @@
  *
  * <refsect2>
  * <title>Example application</title>
- * |[
+ * <informalexample><programlisting language="C">
  * <xi:include xmlns:xi="http://www.w3.org/2003/XInclude" parse="text" href="../../../../tests/examples/level/level-example.c" />
- * ]|
+ * </programlisting></informalexample>
  * </refsect2>
  */
 

gst/spectrum/gstspectrum.c

@@ -90,9 +90,9 @@
  *
  * <refsect2>
  * <title>Example application</title>
- * |[
+ * <informalexample><programlisting language="C">
  * <xi:include xmlns:xi="http://www.w3.org/2003/XInclude" parse="text" href="../../../../tests/examples/spectrum/spectrum-example.c" />
- * ]|
+ * </programlisting></informalexample>
  * </refsect2>
  *
  * Last reviewed on 2011-03-10 (0.10.29)