bug#23179: 25.0.92; Restore `M-,' to continue etags search

[Dmitry Gutov]

On 11.04.2019 23:40, Juri Linkov wrote:

> Currently xref uses grep-like color palette, but its output layout is more like
> multi-occur.  I tried to customize xref colors to match occur-like palette, but
> found that colors are hard-coded, therefore the patch below.

LGTM, please go ahead.

> Another problem:
>
>    5. Files in the output of project-find-regexp are not sorted alphabetically,
>       so currently the result is a mess in random order.

Aren't they in the same order as find-grep outputs them? IOW, rgrep must 
have the same problem. I find it very minor, personally.

We can add sorting here, but that would more or less preclude 
asynchronous generation/rendering of output we'd want to implement someday.