autoconf などが複数存在している

portversion を実行すると，不思議な状況に遭遇した．

# portversion -v
[Updating the portsdb  in /usr/ports ... - 17481 port entries found .........1000.........2000.........3000.........4000.........5000.........6000.........7000.........8000.........9000.........10000.........11000.........12000.........13000.........14000.........15000.........16000.........17000.... ..... done]
apache-2.2.4_2              =  up-to-date with port
autoconf-2.13.000227_6      =  up-to-date with port
autoconf-2.53_4             =  up-to-date with port
autoconf-2.59_3             =  up-to-date with port
autoconf-2.61_2             =  up-to-date with port
autoconf-wrapper-20070404   =  up-to-date with port
automake-1.10_3             =  up-to-date with port
automake-1.4.6_4            =  up-to-date with port
automake-1.5_4,1            =  up-to-date with port
automake-1.6.3              =  up-to-date with port
automake-1.7.9              =  up-to-date with port
automake-1.8.5              =  up-to-date with port
automake-1.9.6_2            =  up-to-date with port

はて，なぜいっぱいあるのだろうか．

id:yusmat さんが保険じゃないかと教えてくれました．感謝！