Fix bug 894: the sign of LDLT was not re-initialized at each call of compute()
(grafted from 3e1f580fdb6c5bf43ad9804f1469ac1e4bb313d6)

--HG--
branch : 3.2
extra : source : 3e1f580fdb6c5bf43ad9804f1469ac1e4bb313d6
Fix bug 859: pexp(NaN) returned Inf instead of NaN

--HG--
branch : 3.2
extra : source : f20b295aa91ebd270b6bfc93871f8e16cd33fe54
Addendum to bug 859: pexp(NaN) for double did not return NaN, also, plog(NaN) did not return NaN.
psqrt(NaN) and psqrt(-1) shall return NaN if EIGEN_FAST_MATH==0

--HG--
branch : 3.2