bug#44983: Truncate long lines of grep output

[Juri Linkov]

> Also see this:
> ,----
> | grep -oE '.{0,20}jQuery.{0,20}' bootstrap.min.js
> `----

But what if the user enters such a regexp as "abc|xyz",
then it will be composed into such command:

  grep -oE '.{0,20}abc|xyz.{0,20}'

that matches either 20 characters before "abc", or 20 characters
after "xyz".  Then needs to add parentheses:

  grep -oE '.{0,20}(abc|xyz).{0,20}'

What is worse is that the whole match is highlighted,
including 20 characters before and after the real match.
So it seems this solution is not perfect.