Update to 3.1.3. Add comment to patch.

Changes since 3.1.2:

    Bug 526 - Fix linear vectorized transversal in linspace.
    Bug 551 - Fix compilation issue when using EIGEN_DEFAULT_DENSE_INDEX_TYPE.
    Bug 533 - Fix some missing const qualifiers in Transpose
    Fix a compilation with CGAL::Gmpq by adding explicit internal:: namespace when calling abs().
    Fix computation of outer-stride when calling .real() or .imag().
    Fix handmade_aligned_realloc (affected conservativeResize()).
    Fix sparse vector assignment from a sparse matrix.
    Fix log(0) with SSE.
    Fix bug in aligned_free with windows CE.
    Fix traits of Map<Quaternion.
    Fix a few warnings (507, 535, 581).
    Enable SSE with ICC even when it mimics a gcc version lower than 4.2
    Workaround gcc-4.7 bug #53900 (too aggressive optimization in our alignment check)

(wiz)