wrapper: add -v/--version option to show version

Prior version numbers were only published as Git tags. Make
a version number available at runtime, too. Also, include the
supported OS releases when showing the version information.

The most recent version number was 2.0. This commit's addition of
previously unsupported options bumps us to 2.1.
PU: wrapper: support? for 10.9

I know nothing about 10.9 (will it even be "10.9""?), but maybe the
"10.6 method" will continue to work there.

I will probably not have the next OS X immediately after public
release (nor in developer beta), so I would appreciate it if someone
could give me a clue as to whether the code change in this commit is
appropriate for the next release (e.g. once any NDA has expired).

    Is the next release actually numbered 10.9?

        Does the output of the command "uname -r" say something like
        13.0?

    Does _vprocmgr_move_subset_to_user still exist?

        In 10.8, you could find it in liblaunch (used by libSystem):

            % nm /usr/lib/system/liblaunch.dylib | grep move_subset
            0000000000005fad T __vprocmgr_move_subset_to_user

    Does it still take (uid_t, const char*, uint64_t) args?

        This has historically only been documented in the the
        opensource.apple.com release of launchd (liblaunch).
        Releases for new OS revs typically lag the actual OS release
        a bit (but usually not too much).

    Is it still effective?

        Does this command:

            echo foo|/usr/bin/pbcopy; ./test daemon=sys move-to-user=10.6 system=/usr/bin/pbpaste; sleep 1

        Have this output?:

            foo
            system(pbpaste) process exited 0

    Is it still needed?

        A bit more open-ended since there are more scenarios to test
        (e.g. ending a login session). The simplest would be
        something like this:

            echo foo|/usr/bin/pbcopy; ./test daemon=sys system=/usr/bin/pbpaste; sleep 1

        It is still necessary if you get this output:

            system(pbpaste) process exited 1