use faster BLAS by default

[JeffBezanson]

Simple linear algebra is likely to be one of the first things people try, and it needs to perform reasonably.
We could use ATLAS, or gotoblas:
http://www.tacc.utexas.edu/tacc-projects/gotoblas2/downloads/
gotoblas is not maintained, but it is already very fast, BSD licensed, and runs everywhere julia runs.

[ViralBShah]

GOTOBlas should be much easier to use. We can perhaps worry about bugs when they are discovered.

[ViralBShah]

Using openblas now.