Propagate the sign of NaNs, so that e.g. -(NaN) evaluates to -NaN.
(emul, eremain, e53toe, e64toe, e113toe, e24toe, esqrt): Likewise.
(make_nan): New arg specifies sign of NaN.  All callers changed.
(eiisneg): New function.
(esqrt): Compute sqrt(-0.0) to be -0.0, not 0.0.

From-SVN: r6511