gst/: Deprecate _type_is_fixed, use _value_is_fixed instead, since the fixedness...

gst/: Deprecate _type_is_fixed, use _value_is_fixed instead, since the fixedness depends on the content.

Original commit message from CVS:
* gst/gstcaps.c: (gst_caps_is_fixed_foreach):
* gst/gstpad.c: (_gst_pad_default_fixate_value),
(_gst_pad_default_fixate_foreach):
* gst/gstvalue.c: (gst_type_is_fixed), (gst_value_is_fixed):
* gst/gstvalue.h:
Deprecate _type_is_fixed, use _value_is_fixed instead, since
in some cases (arrays), the fixedness depends on the content.
* gst/gstqueue.c: (gst_queue_handle_src_query):
Check for availability before doing something.