Bug#1471: diff description straight crib from GNU blurb

[Ian Jackson <iwj10@cus.cam.ac.uk>]

Package: diff
Version: 2.7-3

The diff extended description is
 (a) far too long;
 (b) lacking in information helpful when deciding whether to select
     the package;
 (c) full of information not helpful when deciding whether to install
     the package.

Extended descriptions should be a few short paragraphs.  They should
not give information about how to use a package.  They should describe
what the package is.

The problem has arisen because the diff package extended description
has been copied from the GNU blurb without considering whether that
blurb said the right things.

Ian.