Dlahqr2

As discussed at length in http://forge.scilab.org/index.php/p/arpack-ng/issues/1315/, dneupd is broken when linked with dlahqr that comes from lapack-3.
Until someone knows how to port the code to the new lapack-3 functions, I brought back {d,s}lahqr from lapack-2 into the tree, and renamed them dlahqr2 and slahqr2 so that there is no symbol clash when linking with lapack-3.
I believe this should fix most of the issues observed in issue 1315 above.