- Change length limit 4800 to 4500
 - Fix merge chunk logical error

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Previously @IsAllowed annotation was used.
But I found there is a bug.  Becuase most of annotation based
authorization is depends on PathParser. But PathParser
is rather unstable because of its url parsing method.

So, for the reason, a user who has authorization can not change state of checklist,
except issue author.

This patch fix that problem.