what changes between squid 2.7 and 2.6?

[李开君]

Hello.
        I haven't make squid for a long time .I found it changed a lot. Now I 
want to know the difference between 2.6, 2.7 and 3.0 in stable release.  I know 
that it's coss cache filesystem in R_2.6 than in R_2.5. Thanks.
                                
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李开君