Bugfix: If you use the IPO-pinning feature and edited an IPO that wasn't
highlighted as the current Sequence (current Sequence being a Metastrip),
you'll get obscure crashes, since the code
a) was mistakenly using last_seq
b) didn't test for se->ok != 2, thereby doing double frees on imbufs
Am I the only one, who wants to remove the last_seq global completely... ?