The param_type constructors of each random number distribution should
mirror the constructors of the distribution itself, so make the same
changes w.r.t explicit on default constructors.

	* include/bits/random.h (uniform_real_distribution::param_type)
	(normal_distribution::param_type, lognormal_distribution::param_type)
	(gamma_distribution::param_type, chi_squared_distribution::param_type)
	(cauchy_distribution::param_type, fisher_f_distribution::param_type)
	(student_t_distribution::param_type)
	(bernoulli_distribution::param_type)
	(binomial_distribution::param_type)
	(geometric_distribution::param_type)
	(negative_binomial_distribution::param_type)
	(poisson_distribution::param_type)
	(exponential_distribution::param_type)
	(weibull_distribution::param_type)
	(extreme_value_distribution::param_type): Add non-explicit default
	constructors. Remove default argument for first parameter of explicit
	constructors.
	* include/bits/uniform_int_dist.h
	(uniform_int_distribution::param_type): Likewise.
	* include/ext/random
	(beta_distribution::param_type, rice_distribution::param_type)
	(nakagami_distribution::param_type, pareto_distribution::param_type)
	(k_distribution::param_type, arcsine_distribution::param_type)
	(hoyt_distribution::param_type, triangular_distribution::param_type)
	(von_mises_distribution::param_type)
	(hypergeometric_distribution::param_type)
	(logistic_distribution::param_type)
	(uniform_inside_sphere_distribution::param_type): Likewise.
	(uniform_on_sphere_distribution::param_type): Make default constructor
	non-explicit.
	* testsuite/26_numerics/random/bernoulli_distribution/cons/default.cc:
	Test param_type for non-explicit default constructor.
	* testsuite/26_numerics/random/binomial_distribution/cons/default.cc:
	Likewise.
	* testsuite/26_numerics/random/cauchy_distribution/cons/default.cc:
	Likewise.
	* testsuite/26_numerics/random/chi_squared_distribution/cons/default.cc:
	Likewise.
	* testsuite/26_numerics/random/discrete_distribution/cons/default.cc:
	Likewise.
	* testsuite/26_numerics/random/exponential_distribution/cons/default.cc:
	Likewise.
	* testsuite/26_numerics/random/extreme_value_distribution/cons/default.cc:
	Likewise.
	* testsuite/26_numerics/random/fisher_f_distribution/cons/default.cc:
	Likewise.
	* testsuite/26_numerics/random/gamma_distribution/cons/default.cc:
	Likewise.
	* testsuite/26_numerics/random/geometric_distribution/cons/default.cc:
	Likewise.
	* testsuite/26_numerics/random/lognormal_distribution/cons/default.cc:
	Likewise.
	* testsuite/26_numerics/random/negative_binomial_distribution/cons/default.cc:
	Likewise.
	* testsuite/26_numerics/random/normal_distribution/cons/default.cc:
	Likewise.
	* testsuite/26_numerics/random/piecewise_constant_distribution/cons/default.cc:
	Likewise.
	* testsuite/26_numerics/random/piecewise_linear_distribution/cons/default.cc:
	Likewise.
	* testsuite/26_numerics/random/poisson_distribution/cons/default.cc:
	Likewise.
	* testsuite/26_numerics/random/student_t_distribution/cons/default.cc:
	Likewise.
	* testsuite/26_numerics/random/uniform_int_distribution/cons/default.cc:
	Likewise.
	* testsuite/26_numerics/random/uniform_real_distribution/cons/default.cc:
	Likewise.
	* testsuite/26_numerics/random/weibull_distribution/cons/default.cc:
	Likewise.
	* testsuite/ext/random/arcsine_distribution/cons/default.cc: Likewise.
	* testsuite/ext/random/beta_distribution/cons/default.cc: Likewise.
	* testsuite/ext/random/hoyt_distribution/cons/default.cc: Likewise.
	* testsuite/ext/random/hypergeometric_distribution/cons/default.cc:
	Likewise.
	* testsuite/ext/random/k_distribution/cons/default.cc: Likewise.
	* testsuite/ext/random/logistic_distribution/cons/default.cc: Likewise.
	* testsuite/ext/random/nakagami_distribution/cons/default.cc: Likewise.
	* testsuite/ext/random/normal_mv_distribution/cons/default.cc:
	Likewise.
	* testsuite/ext/random/pareto_distribution/cons/default.cc: Likewise.
	* testsuite/ext/random/rice_distribution/cons/default.cc: Likewise.
	* testsuite/ext/random/triangular_distribution/cons/default.cc:
	Likewise.
	* testsuite/ext/random/uniform_inside_sphere_distribution/cons/default.cc:
	Likewise.
	* testsuite/ext/random/uniform_on_sphere_distribution/cons/default.cc:
	Likewise.
	* testsuite/ext/random/von_mises_distribution/cons/default.cc:
	Likewise.

From-SVN: r261592