docs/manual/: - Explicitely include glib.h.

docs/manual/: - Explicitely include glib.h.

Original commit message from CVS:
patch by: Luc Pionchon  <luc.pionchon@nokia.com>
* docs/manual/basics-helloworld.xml:
* docs/manual/hello-world.fig:
- Explicitely include glib.h.
- Do not use global variables.
- Use g_printerr() instead of g_print().
- Minor formating/renaming to increase readibility.
- Renamed new_pad() to on_pad_added()
- Improved explenatory comments.
- renamed ogg parser to ogg demuxer
- Use "autoaudiosink" instead of "alsasink".
Fixes: #538619