dired-mark-files-containing-regexp: unconsistent behaviour

[Tino Calancha]

Hello,

The doc. string of `dired-mark-files-containing-regexp' is:

"Mark all files with contents containing REGEXP for use in later commands.
A prefix argument means to unmark them instead.
`.' and `..' are never marked."

This string doesn't mention exceptions or required user
customizations:
according with this doc. if the file contains REGEXP, then is marked.

Unfortunately, this function will _not_ mark a file, FILE,
containing REGEXP if:

1) There is a buffer, BUF, visiting FILE.
2) BUF is out of sync with the file, i.e., REGEXP is not in BUF.

*) This behaviour is unconsistent with the doc. string.
*) An user would be aware of 1), 2) just after reading the source code.

I)  I suggest to not use BUF at all: just read always FILE.
II) OTOH, if this function should be kept as it is, then the doc. string
    need to be updated to cover 1), 2) behaviour.

See Bug#22694.

What do you think?

Tino