bug#20728: 25.0.50; grep and grep-find templates should have a place holder for the --color argument

[Juri Linkov]

> And fill it in dynamically during expansion.
>
> This way, the caller can set grep-highlight-matches dynamically, without
> recomputing grep defaults (which is expensive). This is particularly
> relevant on MS-Windows, in semantic-symref-grep-use-template and
> xref-collect-matches.

I guess you need reusing the grep command line for purposes
other than highlighting its matches in the output buffer, right?
Then indeed since on Windows grep fails `isatty' detection
we had to use "--color=always" instead of "--color=auto".
Some time ago additional grep options (including "--color=auto")
were set in env GREP_OPTIONS were they could be easily changed,
but not anymore after 2e4c2fe2787785a421f256541de642976e9bd90b.
So maybe now we should add a place holder for grep options
in the template and use it the same way as we used GREP_OPTIONS.