libs/gst/controller/gstcontroller.*: Clarify the docs of gst_controller_get_value_array(): The array where the values...

Original commit message from CVS:
* libs/gst/controller/gstcontroller.c:
(gst_controller_get_value_array):
* libs/gst/controller/gstcontroller.h:
Clarify the docs of gst_controller_get_value_array(): The array where
the values should be written to must be allocated as there seems to be
no way to get the size of a random GType. This doesn't change any
behaviour. Also fix some typos all over the place and remove an unused,
commented function that is not necessary as g_object_set() could be
used instead.
* tests/check/libs/controller.c: (GST_START_TEST),
(gst_controller_suite):
Add unit test for gst_controller_get_value_array().