We actually still had cases of Meta strip duplication resulting in
non-unique strip names. Quiet surprising this went unoticed for so long. :(
Fixed that bug, and think it was last one (at least, no other case of
SEQ_DUPE_UNIQUE_NAME usage should be broken, I think...), and raised
subversion and updated doversion to run uniquename check on strips on
all previous fileversions.
Note: will have to do that again when merging in 2.8...