Don't leak source caps. Use GST_PTR_FORMAT to log caps, so
we don't need to leak strings from gst_caps_to_string().
No need to use GST_DEBUG_FUNCPTR for vfuncs where the base
class will never look them up (like property getters/setters).
Don't use g_return_*_if_fail() for things that aren't directly
programming errors (by the application developer).
Fixes kate unit test under valgrind.
Only put primary language into GST_TAG_LANGUAGE, and convert to lower case,
ie. only use "en" of "en_GB". This is per our tag documentation and hence
what apps expect. Also add example to kateenc property description so people
know a language code is wanted here.
katedec: Kate decoder (text only)
kateenc: Kate encoder (text and DVD SPU only)
katetag: Kate tagger
kateparse: Kate parser
tiger: Kate renderer using the Tiger rendering library
Fixes#525743.
