Extend direct 3x3 eigenvalues for complex (self-adjoint)

Submitted by Gael Guennebaud @ggael

Assigned to Nobody

Link to original bugzilla bug (#1645)

Description

This is a follow-up of bug #1014 (closed), everything is in title.

Quoting Christoph:

"The computation should work for complex (self-adjoint) matrices as well, after replacing every other m(i,j) by conj(m(i,j)) [which of course can be done implicitly], and knowing that imag(m(i,i))==0."