ext/gio/gstgio.c: Don't generate a new supported protocols list on each call but cache it. It's supposed to be static...

Original commit message from CVS:
* ext/gio/gstgio.c: (_internal_get_supported_protocols),
(gst_gio_get_supported_protocols):
Don't generate a new supported protocols list on each call but cache
it. It's supposed to be static anyway, this way we only leak it once
per process.
* ext/gio/gstgiosink.c: (gst_gio_sink_base_init),
(gst_gio_sink_class_init), (gst_gio_sink_finalize),
(gst_gio_sink_set_property), (gst_gio_sink_get_property),
(gst_gio_sink_start):
* ext/gio/gstgiosink.h:
* ext/gio/gstgiosrc.c: (gst_gio_src_base_init),
(gst_gio_src_class_init), (gst_gio_src_finalize),
(gst_gio_src_set_property), (gst_gio_src_get_property),
(gst_gio_src_start):
* ext/gio/gstgiosrc.h:
API: Add "file" properties where one can set a GFile as source/destination.
Add locking to the properties and use gst_element_class_set_details_simple()
instead of a static GstElementDetails struct.