Const-ify GEnumValue arrays.

Const-ify GEnumValue arrays.

Original commit message from CVS:
* ext/esd/esdmon.c: (gst_esdmon_depths_get_type),
(gst_esdmon_channels_get_type):
* ext/gconf/gstgconfaudiosink.c: (gst_gconf_profile_get_type):
* ext/gdk_pixbuf/pixbufscale.c: (gst_pixbufscale_method_get_type):
* ext/libcaca/gstcacasink.c: (gst_cacasink_dither_get_type):
* ext/shout2/gstshout2.c: (gst_shout2send_protocol_get_type):
* gst/alpha/gstalpha.c: (gst_alpha_method_get_type):
* gst/rtp/gstrtpilbcdepay.c: (gst_ilbc_mode_get_type):
* gst/rtsp/gstrtspsrc.c: (gst_rtsp_proto_get_type):
* gst/videobox/gstvideobox.c: (gst_video_box_fill_get_type):
* gst/videofilter/gstvideoflip.c: (gst_video_flip_method_get_type):
* gst/videomixer/videomixer.c:
(gst_video_mixer_background_get_type):
Const-ify GEnumValue arrays.