bug#46882: 26.3; Let `dired-omit-mode' match lines, as well as file names

[Drew Adams]

I changed the option so its value can also be a var
whose value is such a regexp.

(defcustom dired-omit-lines-regexp nil
  "Regexp matching lines to be omitted by `dired-omit-mode'.
The value can also be a variable whose value is such a regexp.
The value can also be nil, which means do no line matching.

See command `dired-omit-mode' (\\[dired-omit-mode]).

Some predefined regexp variables for Dired, which you can use as the
option value:

* `dired-re-inode-size'
* `dired-re-mark'
* `dired-re-maybe-mark'
* `dired-re-dir'
* `dired-re-sym'
* `dired-re-exe'
* `dired-re-perms'
* `dired-re-dot'
* `dired-re-no-dot'"
  :type `(choice
          (const  :tag "Do not match lines to omit" nil)
          (regexp
            :tag "Regexp to match lines to omit (default omits executables)" 
            :value ,dired-re-exe)
          (restricted-sexp
            :tag "Variable with regexp value (default: `dired-re-exe')"
            :match-alternatives
            ((lambda (obj) (and (symbolp obj) (boundp obj))))
            :value dired-re-exe))
  :group 'dired-x)