bug#4403: 23.1; find-dired: use "find -exec ls -ld {} +" or "find -ls" where available

[trentbuck]

Recent versions of GNU find support the expressions

    find <query> -exec ls -ld {} +

and

    find <query> -ls

I believe these are also part of recent versions of the POSIX spec.

It would be great if M-x find dired RET automatically used these forms
instead of the less efficient

    find <query> -exec ls -ld {} \;

that it currently uses.  It would also mean that the output would line
up better, since

    ls foo bar baz

will try to align the three lines, whereas

    ls foo ; ls bar ; ls baz

won't.