* include/tr1/random (poisson_distribution): Add normal_distribution
member, adjust consistently; minor tweaks and rearrangements of the
arithmetic.
(operator>>(std::basic_istream<>&, poisson_distribution<>&)): Move
out of line.
* include/tr1/random.tcc: Adjust.
* include/tr1/random.tcc (normal_distribution<>::operator()): Minor
tweaks.