Cleaning old packages from pkgsrc/packages/All

How does one clean old packages from pkgsrc ( pkgsrc/packages/All )? I
want to get rid of the old packages but not the current one. Doing
this by hand could be tedious at best.

For example:
In the following list 'vim-share-7.1.87.tgz' is the current package, I
use 'pkg_chk' with the binary options therefor I want to keep the
latest version and remove the old.

...
-rw-r--r--   1 root  wheel   5080640 Jul 29  2006 vim-share-7.0.42.tgz
-rw-r--r--   1 root  wheel   5080750 Sep  3  2006 vim-share-7.0.76.tgz
-rw-r--r--   1 root  wheel   5092100 Sep 10  2006 vim-share-7.0.91.tgz
-rw-r--r--   1 root  wheel   5323781 Sep 29 07:47 vim-share-7.1.116.tgz
-rw-r--r--   1 root  wheel   5323801 Oct 28 06:48 vim-share-7.1.145.tgz
-rw-r--r--   1 root  wheel   5323978 Nov  2 22:54 vim-share-7.1.147.tgz
-rw-r--r--   1 root  wheel   5323991 Nov 28 21:55 vim-share-7.1.161.tgz
-rw-r--r--   1 root  wheel   5321760 Jul  7 06:49 vim-share-7.1.18.tgz
-rw-r--r--   1 root  wheel   5321809 May 19  2007 vim-share-7.1.2.tgz
-rw-r--r--   1 root  wheel   5321769 Jul 15 05:22 vim-share-7.1.28.tgz
-rw-r--r--   1 root  wheel   5323630 Aug 17 21:09 vim-share-7.1.68.tgz
-rw-r--r--   1 root  wheel   5323677 Aug 26 06:19 vim-share-7.1.87.tgz

Apologies if the answer is obvious.

Thanks.

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