verify: fix length check
According to the document added above, we should check L1 == L2, and the
only way to get L1 in all cases is to call "rawsize()", and the only way to
get L2 is to call "revision(raw=True)". Therefore the fix.
Meanwhile there are still a lot of things about flagprocessor broken in
revlog.py. Tests will be added after revlog.py gets fixed.
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