typefindfunctions: lower H.263 typefinder max probability

The typefinder returns LIKELY for as little as one possible
sync and no bad sync (not even taking into account how much
data was looked at for that). It's generally just not fit
for purpose, so should just not return anything like LIKELY
at all ever, even more so since it only recognises one out
of ten H263 files, and likes to mis-detect mp3s as H263.

https://bugzilla.gnome.org/show_bug.cgi?id=700770
https://bugzilla.gnome.org/show_bug.cgi?id=725644
rtspconnection: Fix minor memory leaks in error handling

Fixes https://bugzilla.gnome.org/show_bug.cgi?id=726642
playbin: Drop reference to any source element in NULL state

Drop the reference instead of waiting for either finalize(), or
for a new source when reused. Everyone else already forgot about
the old source.
adder: rework the logic to check if eos has to be sent.

Checking the size available was incorrect, and the infos
for per-pad EOS are available.

Same logic as audiomixer.

fixes: https://bugzilla.gnome.org/show_bug.cgi?id=727025
sdp: guard against address parse errors.
videometa: fix texture_type memcpy size

Coverity 1139589, 1139588