Travis updates

The launchpad buildfarm finally got around to the 64-bit builds of my packages last night, so here is the pull request to make use of them.  The changes are: 

* Install `liblapack` directly now, as the new OpenBLAS package no longer bundles LAPACK with itself.

* Install `patchelf` and don't download/compile `patchelf` if a binary of the correct version already exists in the path.

* Install `openlibm` directly, and allow for users to switch between system-provided `libm`, to system-provided `openlibm` to compiled `openlibm`.

I do seem to be having some trouble with a mysterious liblapack/libarpack problem.  As you can see from this [build log](https://travis-ci.org/staticfloat/julia/jobs/6084024), `libarpack` is complaining about `dlarnv_`. That function is a `liblapack` function, and I've confirmed that it is present in the `liblapack.so` that is shipped by my PPA:
```
julia> dlsym(dlopen(Base.liblapack_name),"dlarnv_")
Ptr{Void} @0x00007f478b346080
```

```
$ lsof -p `pgrep julia` | grep lapack
julia   23005 sabae  mem    REG    8,1  9735312  421829 /usr/lib/lapack/liblapack.so.3.0

$ readelf -Ws  /usr/lib/lapack/liblapack.so.3.0 | grep dlarnv
406: 0000000000352080  3056 FUNC    GLOBAL DEFAULT   11 dlarnv_
```

**EDIT**: I think I may have found the problem; this arpack package was built against an older version of my openblas package, I've uploaded a new version, so it'll be a little while (Estimated 11 hours) until it's ready to compile.