Fix gtk-doc warnings. Also don't misuse api-doc comments for normal comments.

Fix gtk-doc warnings. Also don't misuse api-doc comments for normal comments.

Original commit message from CVS:
* docs/plugins/gst-plugins-bad-plugins-sections.txt:
* examples/app/appsrc-ra.c:
* examples/app/appsrc-seekable.c:
* examples/app/appsrc-stream.c:
* examples/app/appsrc-stream2.c:
* ext/directfb/dfbvideosink.h:
* ext/metadata/gstbasemetadata.c:
* ext/metadata/gstbasemetadata.h:
* ext/metadata/metadata.c:
* ext/metadata/metadataexif.c:
* ext/theora/theoradec.h:
* gst/deinterlace2/gstdeinterlace2.h:
* gst/deinterlace2/tvtime/speedy.c:
* gst/deinterlace2/tvtime/speedy.h:
* gst/deinterlace2/tvtime/vfir.c:
Fix gtk-doc warnings. Also don't misuse api-doc comments for normal
comments.