gst: init taglist gtype to use it in gstvalue

Otherwise it will have a 0 value and GstTagList won't be found
for GstValue functions (serialization/deserialization)

https://bugzilla.gnome.org/show_bug.cgi?id=733131
debugutils: Unref pad template after use

Fixes https://bugzilla.gnome.org/show_bug.cgi?id=733121
Miscellaneous leaks aimed for post 1.4