Fixes for 2.6 test failures, replacing astype(str) with apply(str)
Merge pull request #1535 from bashtage/2-6-fixes

TST: Fixes for 2.6 test failures, replacing astype(str) with apply(str)
ENH: Optimize Cython code. Use scipy blas function pointers.
DOC: Mention arma speed-ups in release notes