arpack.rb: improved BLAS support (both openBLAS and vecLib)

Based on my rather tumultuous experience with vecLib, BLAS, Octave, and all things Fortran this last week, I submit a change to the ARPACK formula.

First, there's no need to specify both ``--with-blas`` and ``--with-lapack``, so I've removed the latter. Having duplicated linker flags seems to confuse libtool, particularly with the "-framework" flag, which it really doesn't handle well anyway. I've seen the duplicated flags cause a permutation of the link order when working on the Octave project.

Secondly, I've added the "-ff2c" flag when linking to vecLib. It's either this or use dotwrp (which is incomplete) or vecLibFort (which isn't approved yet). This is necessary because vecLib exports using the F2C return value convention. The good news is that ARPACK exports only subroutines, so even though we're compiling for F2C, it *will* link with other GFortran code compiled either way.