Storage tokens not properly handled on wrapped CNFS buffers

[Julien-Elie]

Fix 3 bugs reported by Kamil Jońca on CNFS:

• a duplicate entry returned by makehistory on fully wrapped cyclic buffers (the first article of the cyclic buffer appeared twice in the output);
• an untimely removal from history of the first article of a fully wrapped cyclic buffer (expire wrongly thought the storage token of the first article was no longer existing after a wrap);
• an off-by-one cycle number for the first article of the previous cycle number of a cyclic buffer containing articles from two different cycle numbers (makehistory returned the current cycle number for it instead of the previous one).