2017-12-24  Michele Pezzutti <mpezz@tiscali.it>

	PR libstdc++/83237
	* include/bits/random.tcc (poisson_distribution<>::operator()):
	Fix __x = 1 case - see updated Errata of Devroye's treatise.
	* testsuite/26_numerics/random/poisson_distribution/operators/
	values.cc: Add test.
	* testsuite/26_numerics/random/pr60037-neg.cc: Adjust dg-error
	line number.

From-SVN: r255993