[bug-recutils] manual: fix overlong lines and a couple of examples.

[Ralf Wildenhues]

The idiom
  cat file | $filter >> file

is dangerous: when the filter adds enough data, and quickly enough, it
may loop until you run out of space.  Details depend on buffer sizes in
cat and the kernel, and on scheduling timing.  Let's avoid recommending
inherently racy commands, see attached patch.

One solution to issues like this is sponge from the moreutils package
(not GNU, unfortunately).

Cheers,
Ralf

0003-manual-fix-overlong-lines-and-a-couple-of-examples.patch
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