This is very similar to (and directly based on) the test for --help. I think
it's nice to do this: the test is very quick, but it'll catch cases where we
forgot to hook up the option, or forgot to exit after printing --version, and
it'll also increase our test coverage a bit.
Even though many of those scripts are very simple, it is easier to include
the header than to try to say whether each of those files is trivial enough
not to require one.
In a few cases, the prefix was originally necessary because a different helper
script was used for automake, and a different one for meson. But now we use
meson exclusively, and the prefix isn't useful. This also synchronizes the
target name, file name, and variable name in meson.build. The targets exposed
by meson didn't have the prefix, so the user interface is unchanged.
(The prefix is retained in the few tools that are used for meson itself,
e.g. meosn-vcs-tag.sh, meson-make-symlink.sh, etc.)
