First draft of arpack-ng

`arpack-ng` is needed by `octave` to enable the `eigs` function. I have tested this with a manual compilation of both `arpack-ng` and this `octave` revision: http://hg.savannah.gnu.org/hgweb/octave/rev/7c48493d98e1

### Caveat 1
This fails with `brew install arpack-ng` but succeeds with `brew install --env=std arpack-ng`

### Caveat 2
In the `test do` block, I have the following code:

    system "/usr/local/bin/dnsimp --version"
    system "/usr/local/bin/bug_1323 --version"

Those lines will fail. Why?

Because in the original source distribution, these two binaries are used
for testing the compiled libraries:

    TESTS/dnsimp
    TESTS/bug_1323

and they require the file

    TESTS/testA.mtx

I don't think these binaries and test suites are needed in the Homebrew
install.  Is there a way to prevent them from being symlinked in
`/usr/local/bin`?

This is my first Homebrew formula and I do not know any Ruby, so please
bear with me.