bug#48883: dired marking bugs

[Boruch Baum]

In testing my diredc package, I'm coming across the following bugs
reproducable in \emacs -Q -nw:

1) Improper marking of directory heading line

   1.1) The correct and expected behavior of dired is that when one
        navigates to a directory heading line (eg. the first line of a
        simple dired buffer) and presses 'm', all "real" files of that
        directory are marked, [IMPORTANT] the lines for the "not-real"
        files '.' and '..' are not marked, and [IMPORTANT] the directory
        line itself is not marked.

   1.2) Likewise, typing 'u' on that line unmarks all said lines.

   1.3) Now, advance one line, to the line typically presenting a
        summary, beginning with the word 'total', and press the sequence
        'C-u -1 m'.

   1.4) Why is there now a mark on the prior line, the directory line?
        Note that the result differs from actually performing 'm' on
        that line also in that none of the "real" files in the directory
        are marked. Note also that performing 'u' on the line does not
        remove the mark, but performing 'U' on the buffer does.

   1.5) Attempting to perform an operation on the marked directory line
        (eg. 'C' to copy it) returns the message "No files specified"

2) Improper marking of "not-real" files '.' and '..'

   2.1) See paragraph 1.1.

   2.2) However, those lines can be manually marked using the 'm'
        command, and attempting to perform an operation on them (eg. 'C'
        to copy them) returns messaging indicating a willingness to
        overwrite whatever target directory is chosen. I haven't risked
        let it operate.

   2.3) As in paragraph 1.3, it is possible to mark the two lines using
        a negative prefix argument.

3) Improper advancing to (point-max)

   3.1) Marking the final entry in a dired buffer advances POINT to a
        blank line, which is pretty much never desirable to a user.

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